Transit Wireless took to the Yankee Stadium subway station Thursday to announce that it has switched on its first stations in the Bronx and started construction in Brooklyn.

Transit Wireless has been working on a long-running project, which began in 2010, to deploy WiFi and cellular service across the New York Subway system. The fourth phase of this project, announced Thursday, added 21 stations in the Bronx and 16 new stations in Manhattan.

A total of 146 stations are now connected to Transit Wireless network, according to CEO Bill Bayne.

The next 37 stations to go live will be in downtown Manhattan and the first stations in New York's largest borough, Brooklyn.

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In fact, "all the stations downtown are completed," Bayne told Light Reading after the press conference Thursday. This means that the company has installed a neutral host distributed antenna system (DAS) and WiFi hotspots in the stations. AT&T Inc. (NYSE: T), Sprint Corp. (NYSE: S), T-Mobile US Inc. and Verizon Wireless are all up and running on the system, although not all carriers are in all stations. (See Verizon On Board With NYC WiFi Subway Build-Out and Mind the DAS! AT&T & Sprint Aboard Full NYC Subway Project.)

The tricky part of deploying downtown, Bayne explains, is running the fiber that connects to the stations that connects each subway stop to the basestation "hotel" where the Transit Wireless and carrier equipment sits. (See Transit Wireless: Unwiring the NYC Subway for a rundown on how the system works.)

Brooklyn, meanwhile, is very much in the early phases of deployment. Bayne says that the basestation hotel and six stations are under construction. The company has so far deployed 30 miles of fiber in Brooklyn.

The entire project is now due to be completed in 2017.

— Dan Jones, Mobile Editor, Light Reading