MONTPELIER — As part of a four-month trial period, Sprint Wireless customers in Vermont can send a text message to 911 for emergency help.

The service started Monday. Sprint Wireless customers must have mobile phones that are capable of sending text messages. It’s part of a trial to evaluate the technology.

David Tucker, executive director of the Enhanced 911 Board in Vermont, said this is the second such trial launched during the year. He said the fact that a large number of people who are deaf or hard of hearing already use Sprint means officials will be better equipped to provide access for that population to the Vermont 911 system.