AT&T HTC One - SIM Unlocked phone not picking up any other carrier

[jyoungjr]

I have an AT&T HTC One that has been SIM unlocked. I am able to put another SIM from verizon, tmobile or sprint into the phone but I don't get any signal reception at all. I am going to be traveling overseas and want to change my SIM during that time. Anyone have any ideas?