Had exactly the same problem. Had the phone on for less than one hour and did backup ass. and all contacts were there then suddenly no telling why but they were gone. Turned off and back on like mentioned a BLAMO they're back. Thanks guys my wife thinks I'm a real hero. HAHAHAHA

I had the same issue. Just got the phone and did the Verizon contact backup, left the phone for awhile, went back and bammo - no contacts!

I turned the phone off, back on and lo and behold my contacts were back! Maybe we should look for a software update on Casio website, eh?
Later

mine did a similar thing.. I use backup assistant, and when I first had it, it loaded everything and all of a sudden it was gone. I took it in, and the service tech somehow fixed the problem, and I didn't have any issues afterwards

now I'm having an issue with the phone locking up when I try to access the phone's photo album. I can't hit end and take it back to the main screen, rather I have to close the phone and then re-open it to get it to function. The only time the photo album will work is if I power down the phone, turn it back on, and then it works again. VERY frustrating

Anyone have their Casio Exilim C721 just delete the entire contact list?
I just upgraded and luckily had Verizon's Backup Assistant to restore the contacts. Verizon was no help in explaining why it happened.