Random Missing Contacts

I am experiencing the same thing today. I got the iPhone5 with iOS6 the day after it came out. I restored the phone from my latest iPhone 4 backup (not updated to iOS6) and everything has been fine. Today I noticed that I received text from numbers not in my contact list (so a name was not associated) to then realize that these were from people I know, have a lengthy text history with already and actually texted yesterday. So these contacts were in my contact list just yesterday. I've been on iOS6 since I received my phone launch day so this isn't the result of an update. I can't recall changing any settings in the last day or so. I don't want to have to restore from backup. Any suggestions on what the issue could be?

 

I figured my issue out, which may be the same as your girlfriends. I also have an exchange server for work setup on my phone. Today, within outlook, I deleted a bunch of mail contacts - many of them I remember being those that are missing from my phone now (in retrospect I remember wondering to myself how these contacts ended up in my outlook contact list). I'm hoping the way to correct this for the future is to set iCloud as my default contact account (I originally had my work exchange server selected) SETTINGS-MAIL,CONTACT,CALENDERS scroll down to the CONTACTS section and change DEFAULT ACCOUNT to iCloud...
Hopefully