Even though T-Mobile is the last major U.S. carrier without the iPhone, it’s still trying to improve its network to lure in users with unlocked Apple handsets.

The company announced, on its blog, that it’s bringing enhanced coverage and faster speeds for unlocked iPhone users in three metro areas. The enhancements are part of T-Mobile’s $4 billion network improvement plan.

  • Washington D.C.: Alexandria, Va.; Arlington, Va.; Chevy Chase, Md.; Falls Church, Va.; Laurel, Md.; McLean, Va.; and Silver Spring, Md.
  • Baltimore: Glen Burnie and Towson, Md.
  • Houston: Cypress, Jersey Village, Humble, Kingwood, and The Woodlands.

T-Mobile customers in Las Vegas and Kansas City, Mo. have already seen the improvements. The company is also working on the networks in Boston, Chicago, Los Angeles, Miami, Minneapolis, New York metro area, Philadelphia, San Francisco, San Diego, and Seattle.

And the improvements seem to be more than just talk. In internal testing by T-Mobile, an unlocked iPhone 4S running on its HSPA+ network averaged 70 percent faster download speeds than the same handset running on AT&T’s network. And unlike AT&T, T-Mobile also has unlimited data plans.

Interestingly, any mention of the iPhone was recently removed from T-Mobile’s marketing of the “unlocked and unlimited” plans. But it seems that the fourth-largest carrier still wants to bring in unlocked iPhone users from AT&T.