Disappearing contacts from new 4s

Just got a new iphone 4s. I haven't had a chance to upload my entire address book, but some of the contacts I have entered have disappeared. This is the second time this has happened and I haven't even had the phone a week yet. The first time, I thought that I just didn't save the info correctly... but only some of the contacts are missing, not all of them. Can anyone help? I'd like to know what the issue is before I enter all of my contacts. Again, I haven't even plugged the phone into the computer yet, so it cant be a syncing issue. Thanks!