T-Mobile has upgraded its networks in 14 markets including New York City, Boston, and Dallas to support faster data speeds on the iPhone, the company announced today.

The move precedes T-Mobile bringing the iPhone to its network in full force, which will happen next year. But it’s a good move that will help anyone who currently uses an unlocked or jailbroken iPhone on T-Mobile. And it’s a promising sign for T-Mobile users who have been waiting for years for the iPhone to be officially offered and working on T-Mobile’s network.

T-Mobile claims that internal testing showed that “unlocked iPhone 4S devices running over 4G (HSPA+) on our 1900 network recorded on average 70% faster download speeds than iPhone 4S devices on AT&T’s network.” Basically, T-Mobile is saying iPhones running on its network in the 14 new markets should have much faster data speeds than what AT&T is providing.

The network says it will continue to rapidly upgrade its network, with work already started to bring parts of Los Angeles and San Diego up to speed.

Adding to today’s news, contract-free wireless provider Solavei also announced that its customers can tap 4G coverage on unlocked GSM iPhones in T-Mobile’s new markets. Solavei’s service runs $49 a month.

Here’s a full list of T-Mobile markets that will now support the iPhone’s 1900 MHz band:

• New York, including The Bronx, Brooklyn, Manhattan, Queens and Staten Island

• Newark, N.J., including the surrounding cities of East Orange, Elizabeth, Jersey City, North Bergen, Paterson and Union City

• Boston and Cambridge, Mass., including the surrounding cities of Amherst, Andover, Arlington, Bedford, Belmont, Billerica, Braintree, Brockton, Brookline, Burlington, Canton, Chelmsford, Chelsea, Chicopee, Dedham, Everett, Framingham, Hadley, Holbrook, Holyoke, Lawrence, Lexington, Lowell, Ludlow, Lynn, Malden, Marblehead, Medford, Melrose, Metheun, Milton, Nahant, Natick, Needham, Newton, Quincy, Reading, Revere, Salem, Saugus, Sommerville, Stoneham, Swampscott, Tewksbury, Wakefield, Walpole, Waltham, Watertown, Weston, Westwood, Weymouth, Wilmington, Winchester, Winthrop and Woburn

• Springfield, Mass.

• Providence, R.I., including the surrounding cities of Cranston, North Providence, Pawtucket and Warren

• Philadelphia

• Detroit and Warren, Mich., including the surrounding cities of Dearborn, Romulus, Royal Oak, Sterling Heights and Troy

• Dallas, including the surrounding cities of Arlington, Carrolton, The Colony, Denton, Farmers Branch, Flower Mound, Frisco, Garland, Grand Prairie, Irving, Lancaster, Lewisville, McKinney, Mesquite, Plano, Richardson, Rowlett and Southlake

• Fort Worth, Texas, including the surrounding cities of Keller and Mansfield

• Austin, Texas including the surrounding city of Round Rock

• San Antonio

• Tampa, Fla., including the surrounding cities of Clearwater, Largo, Safety Harbor, St. Petersburg and Vinoy Park

iPhone photo via Devindra Hardawar