On a new phone, just give your service your sim card number.
If you get a "Sim not provisioned mm#2" message on a Go phone, it's probably because you have not put money into your account for two months, so they canceled your account. I called ATT today after I got the mm#2 message. (You have to jump through a lot of hoops by the way, so be prepared for at least 20 minutes of being transferred.) They told me they had canceled my account because I might be dead. I told them I was still alive, so they said to go to one of their corporate offices. They gave me the addresses of two offices which were only 2 miles from my house. The man I spoke to put a note on my record that they were to give me a new sim card free. I called the office and they verified that the new sim card would cost nothing, and that it would only take ten minutes to get a new one. All I needed to do was tell them my old Go phone number.
I have to say that I could not find a stipulation anywhere in the ATT literature that said the Go phone account would be canceled if no additional payments were made in a two-month period. It's not on the box, and it wasn't in the manual. I dared the man I spoke to at ATT to find it, but he couldn't. This is a very questionable business practice - especially for a "pay as you need it" plan.