While we were working on an iOS project, the backend service required some kind of device unique ID be uploaded in some special cases. Getting / Generating some sort of unique ID isn’t something difficult. But on iOS platform, it becomes a little “different”. It’s simply because you have more than one option to do it and some of them was allowed but recently got deprecated by Apple.
We made some investigation months ago and recently I found a great article in which all possible options have been listed and explained in detail. Basically, you could choose from “CFUUID”, “NSUUID”, “Advertiser Identifier”, “Identifier for Vendor”, “UDID” and “OpenUDID”. Since it’s already the iOS7 world, you might want to just use “NSUUID” for generating new UUID on every call, or “Advertiser Identifier” and “Identifier for Vendor” for identifying the device.
I suggest you take a look at that article (it’s not very long), try the demo app it provides if you need an unique ID in your iOS application.