T-Mobile, is the only company that does not officially carry the iPHone. But, even that..T-Mobile has more then one million customers using unlocked iPhones on its network. Not all them can use their iPhone on 3G /4G network, tha is why T-Mobile is deploying a 1900 3G/4G HSPA+ network.
Now, according with FierceBroadband Wireless, A T-Mo executive has just said that T-Mobile is not willing to make huge sacrifices to add the iPhone to its portfolio. Sprint , a while ago, paid Apple 15.5 Billion dollars for the ability to sell Apple products like the iPhone and iPad.
We have to wait and see if T-Mobile decide to offer the iPhone or just focus in only offering plans specially for people with unlocked phones, including the iPhone