2012-11-24 17:15 - edited 2012-11-24 17:16
T-Mo, unlike the other big carriers, supports wifi-calling. It's no longer a hardware-on-phone issue since they moved away from straight UMA. So, in its current IMS (they just moved on from Kineto) it can be incorporated in the phone as a software upgrade. PLEASE do this. It allows free calls from anywhere in the world (so long as you have a wifi connection) and allows you to use your own cell number.
As it's a software issue Nokia cannot help you on this one. Microsoft have total control of the software as it's Windows Phone OS. Nokia just provide the hardware.