I was finally able to get my contacts on my phone this afternoon after struggling with it for more time than I'd like to admit. Hopefully this will help if you lost your contacts on the iPhone 4S
I had a iPhone 3GS that I'm giving to my daughter to use as an iPod which I backed up Thursday knowing I'd get the iPhone 4S in the mail the next day. At that time I also updated my iTunes and updated to iOS5. So going into the 4S I thought I had done the "right" things but I'm not sure if it was my mistake or if its a problem with the technology.
Thursday--Updated 3GS to iOS5, iTunes and backed up the 3gs.
Friday--Got the 4S, system was busy so I went to the ATT store and had them activate it. When I got home I hooked up the 4S and got the message to register as a new iPhone then got the message to restore from backup. It went through the whole thing and then gave me a message that it couldn't complete it because that backup was not compatible with the iPhone 4S. I checked and nothing was on the new phone, just my name and my phone number. Hooked up the 3GS because I thought that the backup maybe didn't finalize so I was going to back it up again since everything I needed was still on that phone. That was a mistake, I accidentally reformatted that and now I had NO information on either phone.
Saturday--Searched online and tried numerous things to no avail. I also created an account for the Cloud so I could store contact info that way. I had all my contacts in Outlook (it syncs to Outlook but I've never used it) so I thought I could maybe get them on the Cloud somehow or re-sync the 3GS to get them on there and then back it up again. After that I did LOTS of other things and got to the point where nothing was on the Cloud and my 3GS was able to accept the sync with Outlook. I read something in the forums about messing around with the Cloud and that was finally what worked. In the 3GS, I went to settings and on the Cloud section I turned off the Cloud for mail, contacts, calendars and notes because those were most important to me). Nothing showed up on the 3GS or on the Cloud and I left the settings with those 4 categories set for "no". The 4S was hooked up to the computer and I did the same thing in the settings menu and nothing showed up on either phone or the Cloud. I did it one more time with the 3GS and my contacts were restored! I also left those settings as "no" for the 4S so when I got the info back on the 3GS I immediately changed the settings on the 4S to "yes" and ALL my contacts were there. My voicemail gretting, saved voicemails as well as the call history were all there!
Not sure if that will work for your situation but hopefully it will help