Eseries / Communicators :: E72 - SIM Card Registration Failed

I woke up this morning, my phone was fine, I surfed the internet, checked my messages etc. I then got the bus to work, during the journey the connection dropped (this sometimes happens but it always comes back after 30 secs or so) after a while the phone said "sim card registration failed".

I restarted the phone, no luck. I took the phone apart, removed the sim, put everything back, no luck. I put the sim in another phone, that worked. I put a different sim in my own phone, no luck. I reset the phone to factory settings then put in the sim, no luck. I restored the phone, no luck.