I cant send sms from my nokia 5800 :(?

[Sara]

its been a week i cannot send sms and i did everything i could and its driving me crazy now x(
it sends 3 msgs and then when i try to send the fourth message it goes to the outbox saying resend at *time* and i have to restore the settings from the previous back up i made and it gets ok temporarily, again sends 3 messages n problem comes up with the fourth. I am so sick n tired Im at the verge of throwing this stupid phone
I checked the message center number its fine it doesnt change and i even tried to update the firmware to latest version. PLEASE HELP!! *before i actually smash my phone* which i wudve if it wasnt a gift *sigh*