I'm giving mine to my sister. I think the procedure is:
Turn Find My PHone in setting on the phone
Reset the phone in settings.
Remove the backup, but I can't remember where/how.
What about the SIMM card. I have a T-mobile card in there, but I don't use that service any more. My sister has an old phone on Tmobile phone now, that takes the old, big SIMM. Should I just leave my mini SIMM in my iPhone and can Tmobile transfer her current number to my iPhone? Or does she have to get a new/different mini SIMM for herself? If so, can the Apple Store do this for her or does she have to go to Tmobile?
I believe she'll need to get a new SIM from T-Mobile, it's usually a $20 fee.
Back up your phone via iTunes or iCloud first.
Turn off Find my iPhone in Settings>iCloud next.
Restore iPhone in iTunes to erase your data from phone.
Remove SIM card and have your sister get a new SIM card activated at T-Mobile store.
Remind your sister how kind and wonderful you are for giving her an iPhone
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