You can now text 911 in some parts of the country. Texting while driving, however, is still not a good idea. (AP Photo/LM Otero)

Wireless carriers are giving Americans in emergencies a new way to reach 911: by text message. The Federal Communications Commission program, which is scheduled to have a national rollout by the end of the year, began debuting Thursday in various parts of the country. Here's what you need to know.

What is the program? 

The Text-to-911 program is exactly what it sounds like: It allows you to text 911 dispatchers with information about an emergency rather than place a phone call.

Why would I use this?

In most cases, you should make a voice call when contacting 911. That option tends to be more efficient, particularly in emergency situations when you want to relay a lot of information in a short amount of time. Calling also tends to give dispatchers more accurate location information, though that's not always the case with cellphones (but that's a separate problem the FCC is looking to fix).

The text program is designed to make it easier for people who are deaf, hard-of-hearing or have a speech impediment to communicate  in emergency situations, though the FCC still recommends making a voice call first. It's also useful when the person calling 911 isn't in a position to speak, such as in situations where making a noise would expose someone to greater danger.

How do I use it?

All the major carriers in the United States -- Verizon, AT&T, Sprint and T-Mobile -- are supporting the service. In most cases, you will need a phone plan that allows texting to use the service. All cellphones can make emergency calls, even without a plan, but that's not the case with text messages.

How do I know if my local dispatcher supports it?

While there's widespread carrier support for the program, relatively few dispatch offices have text-to-911 capabilities so far. The FCC has a full list of counties where the service works, including in Frederick Country, Md., and Henry, James City, Southampton and York counties in Virginia. As my Washington Post colleague Brian Fung reported in January, some states, such as Vermont, have also started their own similar experimental programs.

How do I know if my text to 911 got through?

The FCC system is set up to send a bounce-back message to let users know if their text message to 911 doesn't go through. If your dispatcher doesn't support texting, you should get one of these bounce-back messages, which will suggest that you call 911 instead.

If you're curious about whether you're in an area that supports the service, the FCC recommends calling your cellphone provider -- Verizon, AT&T, Sprint or T-Mobile -- to check. The agency also recommends checking in with local state legislators or public safety officials for information.