Post Pay to Flex Pay w/ Change of Responsibility

[MtReload]

I was just wondering, is it possible to go from a post pay plan to a flex pay plan? I'm on a family plan under my step dad's name and I was just wondering if it's possible to do a change of responsibility so I can take my number and everything and go onto my own plan (Flex Pay) under my own name.

Edit: Just called T-Mobile. Turns out you can't do that but I can open a Flex Pay account and have my line on the family plan suspended and just let the contract run out on that.

Amy