Samsung I5503T Every message not sent

Hello, I just bought a new samsung I5503T phone today and used the SIM from my old phone (About 2 years old) and everything works perfectly fine except SMS. Every single message I try to send doesn't even attempt to send, it just says "message not sent" and gives me the little !. I am confused as to why this is so, and if it is because of me re using the SIM or something I have to enable on the phone?