T-Mobile launched the Name ID service on select smart phones Wednesday, becoming the first of the four major U.S. mobile phone companies to have a full caller ID function.

The popular function, which was previously available only on landlines, will use information from a database to provide the name, city, and state for unknown callers. Name ID is engineered by mobile software startup Cequint, and the database information is provided by its parent company, Transaction Network Services.

The Name ID feature is initially available only on the Samsung Exhibit 4G. It will be integrated on other devices, such as the T-Mobile myTouch 4G Slide, later this month. T-Mobile is currently offering a free 10-day trial of the Name ID service for consumers who purchase select new phones. After 10 days, consumers will be asked if they wish to continue to service for $3.99 per month.

The Name ID service allows users to save information from incoming calls, making it easy to add new contact information.

CNN Money points out one obstacle, however: Verizon Wireless withholds the names of its subscribers, so contact information for Verizon users will not appear on Name ID.

Name ID: Know who’s calling—before you pick up [T-Mobile]
Caller ID for cell phones launches on T-Mobile [CNN Money]
Name caller ID introduced to wireless by T-Mobile USA [Market Watch]