[pdxww]

Does it expose any sort of "device id"? Such ids are usually asked for by advertisers and iOS and Android gladly give it to them. I'm sure there are device-id to phone-number maps out there, and anyone with money can get access to them.

[mandeepj]

The device id that you can get via any SDK on ios is not real. And, even if you can get by any other means then Apple would not approve your app.

[cloverich]

Consider _any_ app you've linked your email and phone number to, could (in theory) sell access to your data to any other company that only has your email, and they have both. Or (as another commentor noted) the great many apps that upload your (friends) entire contact list. Consider all the id's, fingerprinting techniques (etc) out there, juxtaposed against the high value that information has (in marketing / ad space) and it seems likely there are many ways to get this information, whether or not you provided it.

[laser]

Unique device IDs are app-specific.