T-Mobile to Sunset MetroPCS's CDMA Network by 2015

Correct me if I'm wrong, but VoLTE phones are just LTE phones with the added ability of pushing voice data over that network...? Wouldn't they then be able to just merge the VoLTE roadmap with TMo's LTE rollout that's supposed to start happening next year?

Or is that something that requires specific tech on the LTE towers to facilitate? Seeing as TMo hasn't built any towers yet, one could see them simply then building VoLTE towers as part of their plan rather than the stock LTE towers they may otherwise have used.