like an OS update? why do some people have problems and some don't?
Well, that is what they are trying to determine, but it is suspected to be in the contacts right now. A corrupt contact is causing some bug. But it could be a multitude of things, that is why apple is working on it, this is not just a select few, it is a good percentage of people, I can promise apple is busting there butts trying to find the cause of this issue, they would rather irradiate the issue swiftly, than replace several thousand phones in store when it may not even help.
Best thing to do os try the restore options like I said earlier, if that does not work than I would proceed with going to the apple store.