At first, VoLTE will be used to deliver "Rich Communications Services" (which look like something similar to what Voice over IP/Video over IP outfits offer today) rather than completely replacing narrowband voice. It will be awhile before Verizon is willing to commit to that, due in part to LTE outages in late 2011.
On the flip side is MetroPC, which has pushed VoLTE as hard as it could.
Then there's Sprint, which will stick to voice over 1x for the foreseeable future, but routes Direct Connect over IP. Sprint's latest DC incarnation seems quite similar to one facet of RCS over LTE.
Well, if they can entice people to get new phones over the next 3 years with a fantastic 5G network, I think this could go a long way to get users off phones that can't essentially forever roam on TMobile's network as well as grabbing customers from VZW/ATT. As TMobile reduces the amount of spectrum on B25/41 users could get frustrated at slower speeds and seek a phone upgrade.