How to disconnect a phone number from an iPhone?

I was given an IPhone but her number is still connected is there any other way I can get rid of her number without having her canceling her contract? Can I get someone to jail break it or something so I can get my number on it? We both have sprint

Remove the SIM card simple!

Replace the SIM crd with a new one, which will have a different number associated with it.

Sprint doesn't have a sim card… Nor does verizon. You can take it to a sprint store and they will do it for you. Thats why i have AT&T and i have a sim