HTC One (M8) - Changing the HTC One Network Connection

Changing the HTC One network connection
HTC One 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.
Video chat and phone calls 175