­T-Mobile USA has announced that Kansas City is the latest market where T-Mobile customers will be able to benefit from enhanced voice and data coverage, as well as faster speeds on unlocked devices, including Apple's iPhone.

The company doesn't sell the iPhone, but says that more than a million unlocked iPhones are working on the network - hence upgrades which are said to be targetting owners of the handset to encourage them to swap networks.

As T-Mobile network advancements continue in other cities, the company said that customers in some parts of Seattle, Los Angeles, Washington D.C. and the New York metro area are already experiencing improved coverage and iPhone "speed sightings" on T-Mobile's HSPA+ based  network.