HTC One Remix - Manual (Page 131)

Changing the HTC One remix network connection
HTC One remix is set to Global mode and connects to the appropriate
network (CDMA or GSM) in your location. In countries where both CDMA
and GSM networks are present, you can select which network to use.
Voice and data roaming charges may apply.
1. Go to Settings, and then tap Call.
2. Tap Preferred Network, and then select the phone network you
want to use.
Phone calls 131