New iCloud - iPhone backup not working

I just converted to iCloud, and my iPad 2 backs up just fine, but my iPhone 4S gets stuck on "Estimating Time Remaining..." The bar never moves. I've left it on for an hour or more, with no change.

There's plenty of storage space, I'm not even close to the limit. I turned off the camera roll backup to see if that would help, and I've tried doing a soft reset, but it still won't back up. Any other ideas before I call AppleCare?

Thanks in advance!