As of today, the four major U.S. wireless carriers (Verizon, AT&T, Sprint and T-Mobile) support the new functionality in "all areas served by their networks where a 911 call center is prepared to receive texts." But the FCC cautions that this does not mean all of the carriers' customers are covered, and for now, "you should not rely on text to reach 911."
To protect consumers, the FCC already requires carriers who don't support 911 texts in certain areas or at all to send automatic bounce-back messages to let senders know that 911 did not receive their messages.
The FCC is encouraging all 911 call centers to accept 911 texts as soon as possible, but it is not mandated, and for now, it's ultimately up to each call center to decide if or when it will start supporting 911 texts.
Today, 911 texts are accepted in limited areas in Colorado, Georgia, Illinois, Indiana, Iowa, Maine, Maryland, Montana, New York, North Carolina, Ohio, Pennsylvania, South Carolina, Texas, Vermont and Virginia.
You can visit the FCC's website for specifics on current locations. And the agency's FAQ page also offers more details on the initiative.
Read more about mobile/wireless in CIO's Mobile/Wireless Drilldown.