Is it allowed to transfer iPhone UDID to my server?

Question

My app has a feature which requires identifying each app users. I'm planning making the app sends UDID to my server. Server stores it, for later use. I don't think that's a personal information, however, I want to know is it approvable or not in Apple's AppStore.

And, including transferring phone numbers. In the case of WhatsApp, it recognizes my friends' numbers automatically. I think that's impossible without some kind of data transfer.

Answer 1

You are allowed to transfer a device's UDID to your servers. That's what it's intended for.

Answer 2

Just make sure that it is no secret what your app does. If it transfers phone numbers to store those on your server then clearly mention this in the app's description or even ask the user for permission the first time.

That actually is a a reason to be rejected I think: not being clear about storing user's data on your own server/service.