I upgraded to iOS 7 yesterday. Today, all my contacts suddenly vanished. They were working in iOS 7 this morning, but have since disappeared.
I'm not syncing contacts with an external system (Exchange, iCloud, Google, etc.). All of the contacts were on my phone only. They are still in my computer's Address Book, but when I sync to the phone and check the Contacts box under "Replace Information on This Phone," no contacts show up on the phone.
Phone favorites and text messages still exist, but as numbers only.
I could manually reenter them, but if there's an underlying problem, I don't want to spend the effort and then lose them again later.
Most Googling has returned no help for the current version. And solutions are to use things like iSync, which doesn't exist on Lion.