Verizon Wireless announced a major text-to-911 push on Thursday, making it the only top-tier operator in the country to offer the emergency service.

Wireless operators have been reticent to deploy text-to-911 because of regulatory uncertainty, lack of preparedness at public service answering points and concerns about liability.

Voice calls remain the preferred way to contact emergency responders, but the ability to send text messages to 911 call centers can be critical for callers who can't make voice calls because they are deaf or would be placed in danger by speaking.

During the 2007 Virginia Tech massacre, students sent SMS messages to 911 about the shooting, only to have them go nowhere.

Verizon plans to make the service, which will run on its CDMA network, available to "select" public safety answer points early next year.

"Our company is continuing its long-standing commitment to address the needs of public safety and our customers by offering another way to get help in an emergency by using wireless technology," said Marjorie Hsu, Verizon Wireless’ vice president of technology.

A spokeswoman declined to specify which markets would get the capability first, but she said Verizon plans to work with public safety officials to let local communities know about the service.

Text-to-911 requires upgrades on both the network side and at public safety answering points. Public safety answering points that receive 911 calls must be able to handle SMS messages, and operators must be able to route SMS messages to 911 service vendors, which in turn route them to responders.

Verizon has used equipment from Intrado for its first two trials. TeleCommunications Systems is providing the gateway for the service announced yesterday.

Verizon has conducted two text-to-911 trials: one in Durham, N.C., and a statewide deployment in Vermont. The operator hasn't talked about results yet, but a public safety official from Durham told Wireless Week in a previous interview that uptake has been limited.

Between August and March, the city only received a single SMS call to 911, and it was a situation that could have been handled by a voice call, said James Soukup, emergency communications director for the city and county of Durham, N.C.

Before Verizon started a trial of the service in Vermont last month, the only statewide text-to-911 service was offered in Iowa by i wireless. The regional operator helped launched the first SMS-enabled 911 call center in Black Hawk County, Iowa, in 2009 and has since expanded the service statewide. It is still the only operator in the state to offer text-to-911.