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.
One thing I do like about T-Mobile is that they really put a lot of energy into taking care of Houston. T-Mobile pulled a bunch of permits from the City of Houston on June 10. Seems like they're not sitting on those permits (which Sprint used to do).
From the few towers I checked, it seems like they are prioritizing towers that were left behind during the 600 Mhz upgrades first. The towers that received the first round of 600 Mhz upgrades have not had any permits submitted.
2.5GHz install on a T-Mobile site in the Houston area: 29.7018566, -95.7397737
Site is only broadcasting two B41 LTE carriers, no N41 as of right now. Talked with the crew for a bit and the four of them are tackling four sites per day right now.