Yes, it is a TMO phone. New from TMO on Monday with the 22.214.171.1240 software on it. UMA worked with that OS version.
It now has 126.96.36.1994 software. I'm tempted to try the 188.8.131.521 beta.
If I could find a copy of the TMO official 184.108.40.2060 software, I would put it back on the device (no, as of a few minutes ago, it was not on the Unsupported Browser