T-Mobile and AT&T launched wireless voice and data service in six heavily-trafficked New York City subway stations and platforms on Tuesday.

T-Mobile and AT&T launched wireless voice and data service in six heavily trafficked New York City subway stations and platforms on Tuesday, but not in its tunnels.

Customers of both carriers will find cell phone reception in the six stations along 14th Street and along the A/C/E lines at 23rd Street. New York's Metropolitan Transportation Authority (MTA) expects to light up the remaining 271 stations within four years.

Transit Wireless—a consortium of four wireless providers incorporated for the sake of building subway station coverage—invested roughly $200 million to fund the project. It has to pay the MTA 50 percent of the revenue it receives each year from "occupancy fees" paid by wireless carriers and other sub-licensees, with a minimum of $3.3 million annually once the build-out is complete.

AT&T and T-Mobile also sank some of the initial costs and paid to rent space from the MTA, which was estimated at $46 million over 10 years.

But for those of you glued to your cell phones, there's a gaping hole in today's announcement: it only covers subway platforms and stations, not cars or tunnels. As one commuter noted, you can already get that in some stations.

According to William A. Bayne Jr., CEO of Transit Wireless, the reasons are simple: money and effort. "I'm guessing it would cost $500 million [to] $1 billion to bring coverage to tunnels too," he said. "It's technically feasible, the problem is cost and logistics."

For instance, Bayne said installation would require shutting down subway tunnels for long periods of time—a problem for the MTA's 24-hour operating hours.

Sprint and Verizon aren't part of the initial launch, but Bayne said he expects the carriers to enter a contract with Transit Wireless in the future.

A Verizon spokesman was vague about future transit plans. "We are always looking for ways to enhance our wireless network, in ways that make sense both for our customers, and our company. We do not comment on rumors or speculation."

The MTA and Transit Wireless have been working on this project since 2004, but its launch was beset with delays due to technical and engineering hurdles, and financing problems.

For more from this morning's event, check out the slideshow above. Also see and ?

Additional reporting by Alex Colon.