I'm doing well with my Tmobile s5 so far on AT&T. I am getting an error when I enable "Wifi calling" which I assume is VoLTE. AT&T solidly covers my area so I know it's available from AT&T. I'm not certain why, since I'm using an AT&T SIM card, that I would get "ER05 - Invalid SIM". My only guess is that the hardware in the Tmobile s5 is set for the Tmobile VoLTE, or that the Tmobile VoLTE is not the same as the AT&T VoLTE. Can anyone clue me in on the technical reasons why this is happening? Best case scenario I just need a new AT&T SIM card.
