Messaging +1 issue

I go into messaging and select a contact to send the msg to. The contact has a phone listed as a 10 digit number. When i hit send, the message fails and the error text says i used an 11 digit number. reason being, a 1 has been placed as a prefix on the mobile number. I can't seem to find how to turn this off. It even happens when I reply to an sms i have received.