Phone log shows numbers not Contact Names after installing Samsung S3 Security Update My Galaxy S3 was working great until I installed a security update yesterday (26/11/12).  Immediately after, the names dropped off the calls list and it is now showing phone numbers only.
Contacted the customer support and they told to hard reboot the mobile. It worked for me. Please backup all your apps, contacts etc using Kies before doing a hard reboot as it will restore the mobile to it's factory settings. It is a pain but had to do it to get my phone back working.