3g and mms messaging

[Foreverrr]

Alright, so I just got my replacement droid the other day in the mail, and everything on it works fine except whenever I try and use 3G instead of wifi, it never works and always says connection failed then if i click retry it just comes back up to connection failed? And i have yet to see the 3G Icon on the notification bar.

Another thing is i am completely unable to send/recieve picture messages, a little message comes up when i try to send one saying "Unable to send message, try again later"

what can i do to change these problems?

thanks