According to an old rumor, AT&T has got only 45 days of exclusivity with Lumia 900, and probably after that other carriers might be able to get Lumia 900 and some might even get a new version of Lumia 900 with 12 MP camera.
Now, there is a fresh rumor doing the rounds about the arrival of Lumia 900 this summer on T-mobile. It seems Andrew from wmpoweruser has been to a T-mobile store where the salesperson insisted that it will indeed come to T-mobile this summer.
I was in my local T-Mobile store talking with one of the store employees about their Windows Phone selection, and he confidently told me without interrogation that the “Lumia 900 will be coming to T-Mobile this summer.”
This confirms a previous rumor back in January 2012, which stated that AT&T only has a 45 day exclusivity period on the Nokia Lumia 900, and that the Lumia 900 coming to other carriers may even have a 12 MP camera instead of the current 8 MP camera.