hi i have a sony erricson w550i, and dont know whats wrong i dont believe alot, as i can send recieve texts, get balance up etc but when i try to call out all i get is the kind of tone you get when dialled a wrong number like der der der .... der der der and no one can call in but can send a text to me........... any tips whats happened!! or if anything been clicked i dont know plzzzzzzzzz help many thanks xx