The following steps are intending for the majority of HTC devices running Android software.
The first thing you will need to do is ensure that 3G/LTE (if you have an LTE device), voice, and text messaging are all working properly on your device. To do this, a Carrier Wipe, and Profile & PRL update are required. Please follow the steps below.
Carrier Wipe
1. Disable Wi-Fi and enable data (some LTE devices do not require this)
2. Open the dialer
3. Dial # # 72786 #
4. Touch "OK", phone will restart
Profile Update
1. Disable Wi-Fi and enable data (some LTE devices do not require this)
2. Touch the “Application” icon
3. Touch Settings icon
4. Touch “System Update” (depending on the device the System Update option may be in the About Phone menu or on the More tab)
5. Touch "Update Profile". The device will restart when complete
PRL Update
1. Disable Wi-Fi and enable data (some LTE devices do not require this)
2. Touch the “Application” icon
3. Touch Settings icon
4. Touch “System updates" (depending on the device the System Update option may be in the 'About Phone' menu or on the 'More' tab)
5. Touch “Update PRL”. Wait for the PRL update to complete, then touch “OK”. Your device may restart after the PRL update. If not, please restart your device.
Once your device restarts, 3G/LTE data, voice, and text messaging should be enabled.
Assuming you are in a 4G capable area, you should be able to use 4G data.