Earlier today, rumors broke out across the net that, according to T-Mobile's support docs, the carrier's branded Nexus 4 will support Wi-Fi calling. Previous statements indicated that the N4 would not have this feature, so we reached out to T-Mobile for official word. Unfortunately, this was an error in the support documents and the phone will not support Wi-Fi calling after all. Here's the official word, directly from T-Mo:

You are correct, just a simple mistake in the online document. No Wi-Fi calling on the Nexus 4. The document link has been updated.

So there you have it, straight from the horse's mouth - no Wi-Fi calling on the Nexus 4. Bummer.