Cant Text

On the 16th I undated my iPhone 3G to OS 3.0, since then texts haven't been sending or receiving as they should. The phone says they have sent but the recipient doesn't get them for an hour or so after. And the other way round. Neither o2 or Apple where any help.

Any ideas 'cos at the moment my £5 phone works better than my £400 iPhone.

Thanks Guys