I was looking at the agreements with both tmo and att for prepaid and it says that you have to activate the number. Then i called the CS and made sure that customers need to do 2 things

1) once you receive the phones then call the customer care back and let them know that you have received the phone ( its called activating the phone)
And
2) make 2/3 phone calls and burn some minutes.

Now do whatever you want to do with you new phone .