Yes, it is a TMO phone. New from TMO on Monday with the 184.108.40.2060 software on it. UMA worked with that OS version.
It now has 220.127.116.114 software. I'm tempted to try the 18.104.22.1681 beta.
If I could find a copy of the TMO official 22.214.171.1240 software, I would put it back on the device (no, as of a few minutes ago, it was not on the Unsupported Browser