Girlfriends had the phone since 20th of November bought it off a mate and it is unlocked (on o2 contract sim)
Since yesterday text message will not send and just sit in the outbox, rang o2 and they advised to clean the sim and if it still doesn't work try a manual network scan.
I've checked the message center number and that is correct and I've sent tried changing send from gprs/3g to via packet data but it still isn't working. Anyone have any advice?

If you have tried turning it off and back on and it still wont send a text then do an hard reset...

http://www.youtube.com/watch?v=VuEnJW3wmaw

That will lose everything though won't it?

yeah, it is a kinda last resort, save what you need to a memory card or back it up on your computer first.

Sweet cheers

i have a N8 you could always try a software update if yours has not been updated for a while i am running symbian ANNA it could free up the messaging without doing a hard re-set,and you should not lose your data.