Wirelessly posted (8520 (220.127.116.111))
Try connecting your device to a computer, and back it up with desktop manager.
Then go to Options/Security/Security wipe.
Tick the emails,contacts etc option, and wipe. Leave the device until the process is finished. Then try and dial. See if it works.
If it does, reconnect your device to desktop manager and click backup/restore and then advanced. Restore all the databases except the options one and you should be sorted.