I'm not sure I believe in this story yet, but there is an article on 9to5google.com that the claimed a T-Mo rep said they are working to get T-Mo's Wifi Calling to work on the Nexus 6.
Google Nexus 6 Release Date on Q4 2014 Confirmed by T-Mobile Featuring Wi-Fi Calling - International Business Times
http://9to5google.com/2014/09/17/t-...ffcalling-working-on-next-generation-nexus-6/
Google Nexus 6 Release Date on Q4 2014 Confirmed by T-Mobile Featuring Wi-Fi Calling - International Business Times
http://9to5google.com/2014/09/17/t-...ffcalling-working-on-next-generation-nexus-6/