I sold someone my iPhone 5 tonight. I erased and restored before selling it. As soon as he put his sim card in it and activated it, his phone number shows up on iMessage. I didn't enable it of course, but I want it gone, and of course I want the buyer to be able to use all the features. I've dissociated the old phone from find my iPhone and my support profile. is there a way to disassociate it from my Apple ID?