After a slow summer, T-Mobile has begun rolling out 3G networks left and right this fall, today announcing aggressive launch plans that will create a UMTS footprint of 27 major markets by year end. By mid-October, T-Mobile will bring eight new markets online, creating a sizable pool for the anticipated launch of its Android mobile phone platform.

T-Mobile and Google are set to unveil in New York next week the HTC Dream, the first phone using the Google-developed Android operating system. The Wall Street Journal has pegged the commercial launch of the phone over T-Mobile’s networks in mid-October, at which point the operator will have 21 radiating markets in its new UMTS/high-speed downlink packet access (HSPA) network.

T-Mobile lit up New York City, northern New Jersey and Long Island in May and over the summer quietly began to roll out other markets. Today T-Mobile has commercial 3G service turned up in Austin, Baltimore, Boston, Dallas, Houston, Las Vegas, Miami, Minneapolis, Phoenix, Portland, San Antonio and San Diego. By mid-October T-Mobile will have added Atlanta, Chicago, Los Angeles, Orlando, Philadelphia, Sacramento, San Francisco and Seattle to that list. And by year end Birmingham, Denver, Detroit, Kansas City, Memphis and Tampa will come online.

As part of the expansion, T-Mobile has also signed new backhaul contracts to provide direct fiber feeds to its cell sites. T-Mobile has signed deals with Bright House Networks, FPL FiberNet, IP Networks and Zayo Bandwidth, which will supply fiber links in Tampa, Orlando, South Florida, San Francisco, Philadelphia and Memphis.

T-Mobile won’t be the only one making a splash with a new network this fall. Sprint is expected to roll out its first WiMAX network this month in Baltimore ahead of its proposed merger of 4G assets with Clearwire. Meanwhile, Verizon Wireless isn’t launching a new network, but it has quietly begun implementing its open-developer program, which allows third-party providers to run applications and devices on its CDMA EV-DO data network. So far, two devices have been certified, a home-monitoring bracelet that uses the CDMA connection to track parolees and those under house arrest and a M2M device for residential meter reading.