Imessage help?

[misskaylen]

Hey folks, I'm using and iPhone 3GS with iOS 5 and I can only receive iMessage messages via email, because the Phone field is filled with the previous phone owner. Is there anyway to change it? I've tried to turn iMessage on and off, i've reseted network settings. When I plug it to the computer, iTunes shows the correct number and the My Number field (in Settings > Phone) shows my correct number too. Thank you.​