When it comes to user-interface design, 911 is about as good as it gets. It’s the “most recognized number in the United States,” Steve Souder, a prominent 911 leader, points out. Simple, fast, and it works from any telephone in the United States. No matter what the emergency is, the call takers on the other side will triage and dispatch assistance.

I’ve taken that ubiquity and simplicity for granted over the past three parts of this EC-1 on RapidSOS as we’ve looked at the startup’s origin story, business and products, as well as its partnerships and business development engine. The company is deeply enmeshed with 911, which means that the prospects of 911 as a system will heavily determine the trajectory of RapidSOS in the coming years, or at least, until its international expansion hits scale and it isn’t so dependent on the U.S. market.

Right now, a $15 billion funding bill to invest in NG911 has been proposed in Congress as part of the LIFT America infrastructure bill that is currently winding its way through the appropriations process and negotiations between Democratic and Republican leaders.

Now, you might think, “911, how could they screw that up?” But this is America, and you’d be surprised.

Despite the daily heroic work of tens of thousands of 911 personnel who keep this brittle system afloat, the reality today is that America’s emergency call infrastructure is in a perilous state. After more than a decade of heavy advocacy, the transition to the “next generation” of 911 (dubbed NG911), which would replace a voice-centric model with an internet-based one designed around data streams, has been trundling along, with some early traction but little universality.

As a Congressional Research Service report described it just a few years ago, “funding has been a challenge, and progress has been relatively slow.” Three years later, the words are just as true as they were then.

Given that RapidSOS’ future ultimately relies on a competent government capable of providing core infrastructure, this fourth and final part of the EC-1 will look at the current state of 911 services and what their prospects are, and finally, how one should ultimately judge RapidSOS given all that we have seen.

911 was invented in the late 1960s to unify America around one emergency number. Early forays to create emergency lines had sprouted up across cities and states, but each used their own system and telephone number, creating massive complications for travelers and people living on jurisdictional boundaries. President Lyndon Johnson’s 1967 crime task force recommended creating a single number for emergency calls as a crime-prevention tool, and on February 16, 1968, the first 911 call was dialed in Haleyville, Alabama.