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 
138,740

7.

Sole Dispositive Power 
0

8.

Shared Dispositive Power
138,740

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
138,740 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)
0.2%

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 
487,590

7.

Sole Dispositive Power 
0

8.

Shared Dispositive Power
487,590

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
487,590 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)
0.8%

12.

Type of Reporting Person (See Instructions)
PN

1.

Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only)
Sirios/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 
952,910

7.

Sole Dispositive Power 
0

8.

Shared Dispositive Power
952,910

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
952,910 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)
1.5%

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 
238,840

7.

Sole Dispositive Power 
0

8.

Shared Dispositive Power
238,840

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
238,840 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 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 
1,292,250

7.

Sole Dispositive Power 
0

8.

Shared Dispositive Power
1,292,250

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
1,292,250 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)
2.1%

12.

Type of Reporting Person (See Instructions)
OO

1.

Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only)
Sirios 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 
85,230

7.

Sole Dispositive Power 
0

8.

Shared Dispositive Power
85,230

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
85,230 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)
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 
111,380

7.

Sole Dispositive Power 
0

8.

Shared Dispositive Power
111,380

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
111,380 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)
0.2%

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 
3,306,940

7.

Sole Dispositive Power 
0

8.

Shared Dispositive Power
3,306,940

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
3,306,940 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)
5.3%

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 
3,306,940

7.

Sole Dispositive Power 
0

8.

Shared Dispositive Power
3,306,940

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
3,306,940 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)
5.3%

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 
3,306,940

7.

Sole Dispositive Power 
0

8.

Shared Dispositive Power
3,306,940

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
3,306,940 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)
5.3%

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

This statement is filed by:

(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, 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 and SA 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:   

138,740

(b)

Percent of class:

0.2%. The percentages used herein and in the rest of Item 4 are calculated based upon the 63,014,444 shares of Common Stock issued and outstanding at July 29, 2005 as reflected in the Company’s Form 10-Q for the fiscal quarterly period ended June 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    

138,740

(iii)

Sole power to dispose or to direct the disposition of   

-0-

(iv)

Shared power to dispose or to direct the disposition of   

138,740

B.

Sirios Capital Partners II, L.P.

(a)

Amount beneficially owned:   

487,590

(b)

Percent of class:

0.8%.

(c)

(i)

Sole power to vote or to direct the vote   

-0-

(ii)

Shared power to vote or to direct the vote    

487,590

(iii)

Sole power to dispose or to direct the disposition of   

-0-

(iv)

Shared power to dispose or to direct the disposition of   

487,590

C.

Sirios/QP Partners, L.P.

(a)

Amount beneficially owned:   

952,910

(b)

Percent of class:

1.5%.

(c)

(i)

Sole power to vote or to direct the vote   

-0-

(ii)

Shared power to vote or to direct the vote    

952,910

(iii)

Sole power to dispose or to direct the disposition of   

-0-

(iv)

Shared power to dispose or to direct the disposition of   

952,910

D.

Sirios Focus Partners, L.P.

(a)

Amount beneficially owned:   

238,840

(b)

Percent of class:

0.4%.

(c)

(i)

Sole power to vote or to direct the vote   

-0-

(ii)

Shared power to vote or to direct the vote    

238,840

(iii)

Sole power to dispose or to direct the disposition of   

-0-

(iv)

Shared power to dispose or to direct the disposition of   

238,840

E.

Sirios Overseas Fund, Ltd.

(a)

Amount beneficially owned:   

1,292,250

(b)

Percent of class:

2.1%.

(c)

(i)

Sole power to vote or to direct the vote   

-0-

(ii)

Shared power to vote or to direct the vote    

1,292,250

(iii)

Sole power to dispose or to direct the disposition of   

-0-

(iv)

Shared power to dispose or to direct the disposition of   

1,292,250

F.

Sirios Overseas Fund II, Ltd.

(a)

Amount beneficially owned:   

85,230

(b)

Percent of class:

0.1%.

(c)

(i)

Sole power to vote or to direct the vote   

-0-

(ii)

Shared power to vote or to direct the vote    

85,230

(iii)

Sole power to dispose or to direct the disposition of   

-0-

(iv)

Shared power to dispose or to direct the disposition of   

85,230

G.

Vitruvius SICAV

(a)

Amount beneficially owned:   

111,380

(b)

Percent of class:

0.2%.

(c)

(i)

Sole power to vote or to direct the vote   

-0-

(ii)

Shared power to vote or to direct the vote    

111,380

(iii)

Sole power to dispose or to direct the disposition of   

-0-

(iv)

Shared power to dispose or to direct the disposition of   

111,380

H.

Sirios Capital Management, L.P.

(a)

Amount beneficially owned:   

3,306,940

(b)

Percent of class:

5.3%.

(c)

(i)

Sole power to vote or to direct the vote   

-0-

(ii)

Shared power to vote or to direct the vote    

3,306,940

(iii)

Sole power to dispose or to direct the disposition of   

-0-

(iv)

Shared power to dispose or to direct the disposition of   

3,306,940

I.

Sirios Associates, L.L.C.

(a)

Amount beneficially owned:   

3,306,940

(b)

Percent of class:

5.3%.

(c)

(i)

Sole power to vote or to direct the vote   

-0-

(ii)

Shared power to vote or to direct the vote    

3,306,940

(iii)

Sole power to dispose or to direct the disposition of   

-0-

(iv)

Shared power to dispose or to direct the disposition of   

3,306,940

J.

John F. Brennan, Jr.

(a)

Amount beneficially owned:   

3,306,940

(b)

Percent of class:

5.3%.

(c)

(i)

Sole power to vote or to direct the vote   

-0-

(ii)

Shared power to vote or to direct the vote    

3,306,940

(iii)

Sole power to dispose or to direct the disposition of   

-0-

(iv)

Shared power to dispose or to direct the disposition of   

3,306,940

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 5% of the class of securities, check the following: o

Item 6.

Ownership of More than Five Percent on Behalf of Another Person

SCM, the investment manager of SCP I, SCP II, SQP, SFP, SOF SOF II and VS, has the power to direct the affairs of SCP I, SCP II, SQP, SFP, SOF I SOF II and VS, including decisions respecting the disposition of the proceeds from the sale of the shares. SA is the general partner of SCM. Mr. Brennan is the sole Managing Member of SA, and in that capacity directs its operations.

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

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.