Can I sell the rights to my sweet grandfathered T-Mobile plan?

[JohnnyK]

My sister has a great T-Mobile plan, but horrible T-Mobile service (surprise!)

Anyway, her plan is the standard $39.99 Get More 600 with 50 loyalty minutes. and free nights when it was an included free promo.

It also was signed when roaming areas (central PA, Carolinas, WI etc) counted as free Mobile-to-Mobile minutes...and she has BUDDYTIME (delicious). and grandfathered $2.99 T-Zones

I know it's possible to do a 'change of billing responsibility' but I'm curious as to the restrictions.

1. Does it have to be in the same area code?
1a. Can it just be in the same market? (in my case Philadelphia--includes its suburbs and rural areas)
1b. Or are there NO restrictions aside from being in the same country?
2. Does it have to be the same number?
3. Is it possible to port the old number out before switching?
4. Anyone want it?

[elevencid]

According to the terms of the change of responsibility form, grandfathered plans and add-ons do not carry over to the new account holder.

[JohnnyK]

Dern.