Until you find your way around — i.e. hack the system — T-Mobile’s Nexus 4 won’t allow for Wi-Fi calling. The information comes from TMOnews, which is best-known for following every step the Magenta carrier takes.
Not sure why this was needed, but what do I know. Guess T-Mobile don’t mind people bringing their own Nexus devices to the network, since we can’t advise anyone to grab Google’s latest phone from the Deutsche Telekom-owned operator. Getting an unlocked unit and using it with a plan that works for you is a much better solution, or so we think… and we love our phones unlocked and capable of handling Skype talks every now and then…