Give props to the AP's Bruce Meyerson for his coverage of T-Mobile and the VoWiFi plans.
I've been asking T-Mobile either face to face or by email about this, as well as posing the question to their representatives at CTIA as this story was something I've been aware of since February and actually began bringing this to light back in April but T-Mobile refused to talk about this at all. GigaOm had some coverage on this back in September and August too, giving credit where credit is due for my being as Om says, "on the job."
Why? Good question. If any carrier in the USA has a converged services perspective it's T-Mobile.
Check out the official info on the parent DT press portal.
If you read through the PDF file you will see something called "Your Network." This is where I suspect that the Fixed Mobile Convergence play will fall into.