UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13G

(Rule 13d-102)

o

Rule 13d-1(b)

ý

Rule 13d-1(c)

o

Rule 13d-1(d)

CUSIP No. 86722Q108

1.

Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only)
Sirios Capital Partners, L.P.

2.

Check the Appropriate Box if a Member of a Group (See Instructions)

(a)

ý

(b)

o

3.

SEC Use Only

4.

Citizenship or Place of Organization
Delaware

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With

5.

Sole Voting Power
0

6.

Shared Voting Power 
71,440

7.

Sole Dispositive Power 
0

8.

Shared Dispositive Power
71,440

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
71,440 shares

10.

Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o
Not Applicable

11.

Percent of Class Represented by Amount in Row (9)
0.1%

12.

Type of Reporting Person (See Instructions)
PN

1.

Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only)
Sirios Capital Partners II, L.P.

2.

Check the Appropriate Box if a Member of a Group (See Instructions)

(a)

ý

(b)

o

3.

SEC Use Only

4.

Citizenship or Place of Organization
Delaware

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With

5.

Sole Voting Power
0

6.

Shared Voting Power 
251,590

7.

Sole Dispositive Power 
0

8.

Shared Dispositive Power
251,590

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
251,590 shares

10.

Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o
Not Applicable

11.

Percent of Class Represented by Amount in Row (9)
0.4%

12.

Type of Reporting Person (See Instructions)
PN

1.

Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only)
Sirios/QP Partners, L.P.

2.

Check the Appropriate Box if a Member of a Group (See Instructions)

(a)

ý

(b)

o

3.

SEC Use Only

4.

Citizenship or Place of Organization
Cayman Islands

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With

5.

Sole Voting Power
0

6.

Shared Voting Power 
489,540

7.

Sole Dispositive Power 
0

8.

Shared Dispositive Power
489,540

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
489,540 shares

10.

Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o
Not Applicable

11.

Percent of Class Represented by Amount in Row (9)
0.8%

12.

Type of Reporting Person (See Instructions)
PN

1.

Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only)
Sirios Focus Partners, L.P.

2.

Check the Appropriate Box if a Member of a Group (See Instructions)

(a)

ý

(b)

o

3.

SEC Use Only

4.

Citizenship or Place of Organization
Cayman Islands

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With

5.

Sole Voting Power
0

6.

Shared Voting Power 
83,900

7.

Sole Dispositive Power 
0

8.

Shared Dispositive Power
83,900

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
83,900 shares

10.

Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o
Not Applicable

11.

Percent of Class Represented by Amount in Row (9)
0.1%

12.

Type of Reporting Person (See Instructions)
PN

1.

Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only)
Sirios Overseas Fund, Ltd.

2.

Check the Appropriate Box if a Member of a Group (See Instructions)

(a)

ý

(b)

o

3.

SEC Use Only

4.

Citizenship or Place of Organization
Cayman Islands

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With

5.

Sole Voting Power
0

6.

Shared Voting Power 
647,140

7.

Sole Dispositive Power 
0

8.

Shared Dispositive Power
647,140

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
647,140 shares

10.

Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o
Not Applicable

11.

Percent of Class Represented by Amount in Row (9)
1.0%

12.

Type of Reporting Person (See Instructions)
OO

1.

Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only)
Sirios Overseas Fund II, Ltd.

2.

Check the Appropriate Box if a Member of a Group (See Instructions)

(a)

ý

(b)

o

3.

SEC Use Only

4.

Citizenship or Place of Organization
Cayman Islands

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With

5.

Sole Voting Power
0

6.

Shared Voting Power 
43,440

7.

Sole Dispositive Power 
0

8.

Shared Dispositive Power
43,440

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
43,440 shares

10.

Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o
Not Applicable

11.

Percent of Class Represented by Amount in Row (9)
0.1%

12.

Type of Reporting Person (See Instructions)
OO

1.

Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only)
Vitruvius SICAV

2.

Check the Appropriate Box if a Member of a Group (See Instructions)

(a)

ý

(b)

o

3.

SEC Use Only

4.

Citizenship or Place of Organization
Luxembourg

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With

5.

Sole Voting Power
0

6.

Shared Voting Power 
58,180

7.

Sole Dispositive Power 
0

8.

Shared Dispositive Power
58,180

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
58,180 shares

10.

Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o
Not Applicable

11.

Percent of Class Represented by Amount in Row (9)
0.1%

12.

Type of Reporting Person (See Instructions)
OO

1.

Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only)
Sirios Capital Management, L.P.

2.

Check the Appropriate Box if a Member of a Group (See Instructions)

(a)

ý

(b)

o

3.

SEC Use Only

4.

Citizenship or Place of Organization
Delaware

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With

5.

Sole Voting Power
0

6.

Shared Voting Power 
1,645,230

7.

Sole Dispositive Power 
0

8.

Shared Dispositive Power
1,645,230

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
1,645,230 shares

10.

Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o
Not Applicable

11.

Percent of Class Represented by Amount in Row (9)
2.6%

12.

Type of Reporting Person (See Instructions)
IA, PN

1.

Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only)
Sirios Associates, L.L.C.

2.

Check the Appropriate Box if a Member of a Group (See Instructions)

(a)

ý

(b)

o

3.

SEC Use Only

4.

Citizenship or Place of Organization
Delaware

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With

5.

Sole Voting Power
0

6.

Shared Voting Power 
1,645,230

7.

Sole Dispositive Power 
0

8.

Shared Dispositive Power
1,645,230

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
1,645,230 shares

10.

Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o
Not Applicable

11.

Percent of Class Represented by Amount in Row (9)
2.6%

12.

Type of Reporting Person (See Instructions)
OO

1.

Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only)
John F. Brennan, Jr.

2.

Check the Appropriate Box if a Member of a Group (See Instructions)

(a)

ý

(b)

o

3.

SEC Use Only

4.

Citizenship or Place of Organization
United States

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With

5.

Sole Voting Power
0

6.

Shared Voting Power 
1,645,230

7.

Sole Dispositive Power 
0

8.

Shared Dispositive Power
1,645,230

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
1,645,230 shares

10.

Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o
Not Applicable

11.

Percent of Class Represented by Amount in Row (9)
2.6%

12.

Type of Reporting Person (See Instructions)
IN

Item 1.

(a)

Name of Issuer
The name of the issuer is Suncom Wireless Holdings, Inc. (the “Company”).

(b)

Address of Issuer’s Principal Executive Offices
The Company’s principal executive offices are located at 1100 Cassatt Road, Berwyn, Pennsylvania 19312.

Item 2.

(a)

Name of Person Filing

(i) Sirios Capital Partners, L.P., a Delaware limited partnership (“SCP I”), with respect to the shares of Class A Common Stock directly owned by it;

(ii) Sirios Capital Partners II, L.P., a Delaware limited partnership (“SCP II”), with respect to the shares of Class A Common Stock directly owned by it;

(iii) Sirios/QP Partners, L.P., a Cayman Islands exempted limited partnership (“SQP”), with respect to the shares of Class A Common Stock directly owned by it;

(iv) Sirios Focus Partners, L.P., a Cayman Islands exempted limited partnership (“SFP”), with respect to the shares of Class A Common Stock directly owned by it;

(v) Sirios Overseas Fund, Ltd., a Cayman Islands company (“SOF I”), with respect to the shares of Class A Common Stock directly owned by it;

(vi) Sirios Overseas Fund II, Ltd., a Cayman Islands company (“SOF II”), with respect to the shares of Class A Common Stock directly owned by it;

(vii) Vitruvius SICAV, a Société d’Investissement à Capital Variable organized under the laws of Luxembourg (“VS”), with respect to the shares of Class A Common Stock directly owned by it;

(viii) Sirios Capital Management, L.P., a Delaware limited partnership (“SCM”), which serves as investment manager to SCP I, SCP II, SQP, SFP, SOF I, SOF II, and VS, with respect to the shares of Class A Common Stock directly owned by SCP I, SCP II, SQP, SFP, SOF I, SOF II, and VS;

(ix) Sirios Associates, L.L.C., a Delaware limited liability company (“SA”), which is the general partner of SCM, with respect to the shares of Class A Common Stock directly owned by SCP I, SCP II, SQP, SFP, SOF I, SOF II, and VS; and

(x) John F. Brennan, Jr., sole managing member of SA, with respect to the shares of Class A Common Stock directly owned by SCP I, SCP II, SQP, SFP, SOF I, SOF II, and VS.

The foregoing persons are hereinafter sometimes collectively referred to as the “Reporting Persons.” Any disclosures herein with respect to persons other than the Reporting Persons are made on information and belief after making inquiry to the appropriate party.

(b)

Address of Principal Business Office or, if none, Residence
The address of the business office of SCP I, SCP II, SCM, SA and Mr. Brennan is One International Place, Boston, Massachusetts 02110-2649.  The address of the registered office of the SQP, SFP, SOF I and SOF II is c/o Goldman Sachs (Cayman) Trust, Limited, 2nd Floor, Harbour Centre, P.O. Box 896, George Town, Grand Cayman, Cayman Islands, B.W.I.  The address of the registered office of VS is 11, rue Aldringen, L-1118, Luxembourg.

(c)

Citizenship
SCP I, SCP II and SCM are limited partnerships organized under the laws of the State of Delaware. SQP and SFP are exempted limited partnerships organized under the laws of the Cayman Islands. SOF I and SOF II are companies organized under the laws of the Cayman Islands. SA is a limited liability company organized under the laws of the State of Delaware. VS is a “Société d’Investissement à Capital Variable” organized under the laws of Luxembourg.  Mr. Brennan is a United States citizen.

(d)

Title of Class of Securities
Class A Common Stock, par value $0.01 per share (the “Common Stock”).

(e)

CUSIP Number
CUSIP No. 86722Q108

Item 3.

If this statement is filed pursuant to §§240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:

(a)

o

Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o).

(b)

o

Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c).

(c)

o

Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c).

(d)

o

Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C 80a-8).

(e)

o

An investment adviser in accordance with §240.13d-1(b)(1)(ii)(E);

(f)

o

An employee benefit plan or endowment fund in accordance with §240.13d-1(b)(1)(ii)(F);

(g)

o

A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);

(h)

o

A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);

(i)

o

A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);

(j)

o

Group, in accordance with §240.13d-1(b)(1)(ii)(J).

Not Applicable

Item 4.

Ownership

Provide the following information regarding the aggregate number and percentage of the class of securities of the issuer identified in Item 1.

A.            Sirios Capital Partners, L.P.

(a)

Amount beneficially owned:   

71,440

(b)

Percent of class:   

0.1%.

The percentages used herein and in the rest of Item 4 are calculated based upon the 62,983,940 shares of Common Stock issued and outstanding as of October 31, 2005 as reflected in the Company’s Form 10-Q for the fiscal quarterly period ended September 30, 2005.

(c)

Number of shares as to which the person has:

(i)

Sole power to vote or to direct the vote   

-0-

(ii)

Shared power to vote or to direct the vote    

71,440

(iii)

Sole power to dispose or to direct the disposition of   

-0-

(iv)

Shared power to dispose or to direct the disposition of   

71,440

B.            Sirios Capital Partners II, L.P.

(a)

Amount beneficially owned:   

251,590

(b)

Percent of class:   

0.4%

(c)

Number of shares as to which the person has:

(i)

Sole power to vote or to direct the vote   

-0-

(ii)

Shared power to vote or to direct the vote    

251,590

(iii)

Sole power to dispose or to direct the disposition of   

-0-

(iv)

Shared power to dispose or to direct the disposition of   

251,590

C.            Sirios/QP Partners, L.P.

(a)

Amount beneficially owned:   

489,540

(b)

Percent of class:   

0.8%

(c)

Number of shares as to which the person has:

(i)

Sole power to vote or to direct the vote   

-0-

(ii)

Shared power to vote or to direct the vote    

489,540

(iii)

Sole power to dispose or to direct the disposition of   

-0-

(iv)

Shared power to dispose or to direct the disposition of   

489,540

D.            Sirios Focus Partners, L.P.

(a)

Amount beneficially owned:   

83,900

(b)

Percent of class:   

0.1%

(c)

Number of shares as to which the person has:

(i)

Sole power to vote or to direct the vote   

-0-

(ii)

Shared power to vote or to direct the vote    

83,900

(iii)

Sole power to dispose or to direct the disposition of   

-0-

(iv)

Shared power to dispose or to direct the disposition of   

83,9000

E.             Sirios Overseas Fund, Ltd.

(a)

Amount beneficially owned:   

647,140

(b)

Percent of class:   

1.0%

(c)

Number of shares as to which the person has:

(i)

Sole power to vote or to direct the vote   

-0-

(ii)

Shared power to vote or to direct the vote    

647,140

(iii)

Sole power to dispose or to direct the disposition of   

-0-

(iv)

Shared power to dispose or to direct the disposition of   

647,140

F.             Sirios Overseas Fund II, Ltd.

(a)

Amount beneficially owned:   

43,440

(b)

Percent of class:   

0.1%

(c)

Number of shares as to which the person has:

(i)

Sole power to vote or to direct the vote   

-0-

(ii)

Shared power to vote or to direct the vote    

43,440

(iii)

Sole power to dispose or to direct the disposition of   

-0-

(iv)

Shared power to dispose or to direct the disposition of   

43,440

G.            Vitruvius SICAV

(a)

Amount beneficially owned:    

58,180

(b)

Percent of class:   

0.1%

(c)

Number of shares as to which the person has:

(i)

Sole power to vote or to direct the vote   

-0-

(ii)

Shared power to vote or to direct the vote    

58,180

(iii)

Sole power to dispose or to direct the disposition of   

-0-

(iv)

Shared power to dispose or to direct the disposition of   

58,180

H.            Sirios Capital Management, L.P.

(a)

Amount beneficially owned:   

1,645,230

(b)

Percent of class:   

2.6%

(c)

Number of shares as to which the person has:

(i)

Sole power to vote or to direct the vote   

-0-

(ii)

Shared power to vote or to direct the vote    

1,645,230

(iii)

Sole power to dispose or to direct the disposition of   

-0-

(iv)

Shared power to dispose or to direct the disposition of   

1,645,230

I.              Sirios Associates, L.L.C.

(a)

Amount beneficially owned:   

1,645,230

(b)

Percent of class:   

2.6%

(c)

Number of shares as to which the person has:

(i)

Sole power to vote or to direct the vote   

-0-

(ii)

Shared power to vote or to direct the vote    

1,645,230

(iii)

Sole power to dispose or to direct the disposition of   

-0-

(iv)

Shared power to dispose or to direct the disposition of   

1,645,230

J.             John F. Brennan, Jr.

(a)

Amount beneficially owned:   

1,645,230

(b)

Percent of class:   

2.6%

(c)

Number of shares as to which the person has:

(i)

Sole power to vote or to direct the vote   

-0-

(ii)

Shared power to vote or to direct the vote    

1,645,230

(iii)

Sole power to dispose or to direct the disposition of   

-0-

(iv)

Shared power to dispose or to direct the disposition of   

1,645,230

Item 5.

Ownership of Five Percent or Less of a Class

If this statement is being filed to report the fact that as of the date hereof the reporting person has ceased to be the beneficial owner of more than five percent of the class of securities, check the following   ý.

Item 6.

Ownership of More than Five Percent on Behalf of Another Person

Not Applicable

Item 7.

Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on By the Parent Holding Company or Control Person

Not Applicable

Item 8.

Identification and Classification of Members of the Group

Not Applicable

Item 9.

Notice of Dissolution of Group

Not Applicable

Item 10.

Certification

Each of the Reporting Persons hereby makes the following certification:

By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect.

/s/ John F. Brennan

John F. Brennan, Jr., individually, and as sole managing
member of Sirios Associates, L.L.C., the general partner of
Sirios Capital Management, L.P., the investment manager of
Sirios Capital Partners, L.P., Sirios Capital Partners II, L.P.,
Sirios/QP Partners, L.P., Sirios Overseas Fund, Ltd., Sirios
Overseas Fund II, Ltd., and Sirios Focus Fund, L.P. and the
investment adviser of Vitruvius SICAV.

/s/ John F. Brennan, Jr.

John F. Brennan, Jr., individually, and as sole managing
member of Sirios Associates, L.L.C., the general partner of
Sirios Capital Management, L.P., the investment manager of
Sirios Capital Partners, L.P., Sirios Capital Partners II, L.P.,
Sirios/QP Partners, L.P., Sirios Overseas Fund, Ltd., Sirios
Overseas Fund II, Ltd., and Sirios Focus Fund, L.P. and the
investment adviser of Vitruvius SICAV.