Can't access the hidden menu on a Tmobile V60 so it can run on AT&T.

I need to access the hidden menu to turn on voLTE setting on my unlocked Tmobile phone. Have tried a couple of different codes and none of them have worked. When I type in #546368#600# I get an AT&T error message "Connection problem or invalid MMI code." I think I should have tried this before putting my old AT&T sim in the phone and transfered all my old G8 phones info over to the V60 maybe. I have a second new V60 I can try this theory on before restoring the factory settings on the phone I have transferred over to, but I want to be sure this is eventually going to work, so has anyone successfully turned an unlocked Tmobile phone into an AT&T phone?