1. Turn Wi-Fi off and Mobile Data on
- Settings > Wi-Fi > Off
- Settings > Data Usage > Mobile Data > On
2. Check signal strength (3 bars, or 60% is recommended)
3. From the dial pad enter ##72786# (press "ok" when prompted)
4. The cellphone is going to update the Profile and the PRL and reboot automatically. That should take about 5 minutes, and then calls and data services should work.
Additionally, you can also perform the steps below:
Clear cache / cookies / history