Why does my iPhone keep prompting me for my Apple ID? For approximately the last week or so, my iPhone 4S seems to have developed a behavior whereby it keeps prompting me for my Apple ID password on roughly 50% of the occassions when I turn it on, and sometimes at other times too. There doesn't seem to be any consistent pattern. Whether I enter my password, or hit cancel, doesn't seem to make a difference.

What might cause this? What are good ways to diagnose or figure out what might be going on, ideally without too much disruption? (e.g. wiping the phone).

I am using iOS 6.1.3.
It seems this was a Skype issue due to "half-purchased" credit. Uninstalling and reinstalling Skype fixed it.