Sorry to be dense - but do you mean by restart - switch off and switch on again in 30 minutes?
I have done that and have sent a message to States but no reply to date...will keep you updated....
A sim card change could help if all other options are ruled out usually sim cards can cause problems like these.
Any solution yet, this has also started happening to me. Again!! The last time it happened, i got over 300 messages in one go, (10 copies of each message) from up to a week old and my phone was recieving messages constantly for over an hour. 02 forum said that there was a problem with sms over that particular weekend, but now only 3 weeks later it is happening again! Although could be worse, meteors solution was to tell my gf that maybe i have blocked her number!!!