I would like a way to uniquely identify users, but as I've learned, Apple won't let you take the user's phone number without asking, nor can you use the UDID anymore, etc. Is there any data I am allowed to take from the phone to uniquely identify our users server-side? (I want to avoid prompting the user for information, for ease and simplicity)
At the very least, is there a way to know when an iphone changes owners; so I can erase app data from the previous owner?