Upgraded to iOS6 and Face Time disappeared

It should still appear but there is no app icon of course. Go to one of your contacts and scroll right down. one of the buttons there should be facetime

Reset Home Screen

On your Device, open Settings, then navigate to “General” in the left-hand pane. Scroll down and tap Reset, then select “Reset Home Screen Layout.”

Reset All Settings

Reset all settings on Device. On your Device, open Settings, then navigate to “General” in the left-hand pane. Scroll down and tap Reset, then select “Reset All Settings.” This will delete any stored WiFi passwords and Appleid login information, but can result in a more stable function. On the final screen you will restore your backup or “Setup as new device” to keep current info intact.

You realize that there is no FT app/icon on an iPhone and that it's accesssed via Contacts?

http://support.apple.com/kb/HT4319