I am building a cross platform application in which devices will communicate with a WCF Service. When a device connects to the service for the first time. I want to have a unique identifier for that device like a GUID and save information to a database. I wanted to use the IMEI but I am reading that iOS does not allow you to access that anymore. Is there a way to store something on the device itself that even if they delete your app and then install it again, you can use the same unique ID like a GUID or something such that when it connects to my service I can identify it as already connected before.