Sending text messages, i can recieve messages but not send them. it keeps telling me to check message centre number, but i cant find it in my phone.

THe message center number if located mostly in messages->settings->center number.
also there is an option like "send via same center" try checking and unchecking it.
Tell the model to be more specific.
You can always get the msg center number from the service provider helpline(customer care)