In order to get your data working again after an outage of 3G or 4G you need to do the following in sequence:
- Phone this number: ##3283#
- Hit "EDIT" - it will prompt for a password
- Hit 287804
- Hit "OK"
- Select "DATA PROFILE"
- Go to Menu --> Restore
- Hit "OK" [Twice]
It will reboot, and do stuff...
Then, once it has fully rebooted, go to: Menu/Settings/System Updates/Update Profile
Once that is done, your data connection via 3G or 4G should be repaired.