To much fanfare, the Federal Communications Commission announced that nationwide text-to-911 service has hit the market in the spring of 2014. But the devil's in the details. You might not have access to the emergency service, even if you have a cell phone carrier who appears to support it.
If you're trapped in an emergency where you can't speak, you can send a text message to 911 and a dispatcher will reply with in kind by text -- if (and this is a big if!) both your carrier and your community support the technology. Note, though, that 911 texts don't get priority over other text traffic.
The four major cell carriers in the United States -- Verizon, AT&T, T-Mobile and Sprint -- support text-to-911 service right now. By agreement with the FCC, the carriers began providing the service within their coverage areas on May 15, 2014.
The Big Four cell providers support the service, but each individual 911 call center determines if and when it will accept text messages. There's no national deployment plan; each community sets its own standards and timetables, so coverage across the country will be spotty for years to come.
In an emergency situation, texting might not be the best way of summoning help if you have reasonable alternatives, like placing a call to 911. Dispatchers rely on cues like tone of voice and speech coherence to gauge the severity of the emergency. Plus, a dispatcher can ask follow-up questions that, if texted, add seconds or minutes to the process -- time you might not be able to sacrifice.
Early rollouts are still very limited; only a handful of jurisdictions nationwide have activated text-to-911 service. The FCC maintains a list of active communities, but as of May 2014, you have better odds of actually needing 911 than of living in a place that's already deployed the system.
The text-to-911 program relies on the Short Messaging Service (SMS) protocol. That means you get plain text only -- no videos, no pictures, no sound clips. And no emoji, either.
On the bright side, if you need emergency assistance in an area that doesn't support text-to-911 capabilities, your carrier (if it supports the service) will reply with a bounce-back message telling you to get help the old-fashioned way -- by voice.