For emergencies when a phone call is impossible, AT&T, Sprint, T-Mobile and Verizon have launched 911 text capability in some markets and should roll out the service nationwide by the end of the year.

The initiative, which was first proposed in 2012, allows people to get help by putting 911 as the phone number and their location and emergency in the text body, NBC News reported. Call centers have been set up to receive and respond to the messages.

While the service can be especially helpful for those with disabilities, texting 911 should be a last resort if calling is not an option.

"Always contact 911 by making a voice call, if you can," said the Federal Communications Commission, as quoted by NBC News. The agency also recommended that those who are deaf or have speech disabilities use "a TTY or a telecommunications relay service, if possible."

Calling 911 allows a dispatcher to ask more questions if necessary before sending help. Texts can also be delayed. If a text doesn't go through, people should receive a "bounce back" message to let them know.

So far, texting to 911 is available in states ranging from Montana to Pennsylvania to South Carolina. A list of text to 911 deployments can be found here.  

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