Following tightly on the heels of Windows Phone 8.1 and new hardware from Nokia, T-Mobile and AT&T have both announced they will carry the Lumia 635. T-Mobile is trumpeting the availability of the Lumia 635 on its network as a solid step from the Lumia 521, which it saw massive success with, while AT&T sees this as one more device in a long line of Windows Phones it carries.
The Lumia 635 on T-Mobile and AT&T will pack the same 4.5-inch ClearBlack display, have LTE network capabilities and surely have a budget-level price. We sadly don't have any specific pricing or availability information outside of "this summer" for T-Mobile and an "intent to carry" (whatever that means) from AT&T.
We do know that the Lumia 635 will be available from both T-Mobile's postpaid service and under the MetroPCS prepaid brand, and we can assume it could be low-end enough to grace AT&T's prepaid carriers as well.