Cleaning up a T-Mobile To Go cell for a new owner

I am selling my Samsung SGH X495 T-Mobile To Go phone on eBay,
including the SIM card.
I called T-Mobile and had them take my name off the account. I also
deleted all my contacts
from the phone and the SIM.

What else do I have to do to "clean" this phone? I just want to be
sure the buyer cannot make calls
of some evil nature and have them traced back to me.

Finally, when the buyer calls T-Mobile to re-activate the phone will
he/she get the remaining airtime?
It's not very much, just curious.

TIA

Ed