Several users have reported Wi-Fi problems after updating to iOS 6. Mostly users have reported that the Wi-Fi option was greyed out.
It seems that this bug was a result of Apple’s servers being down for a short time. It has been further reported that this bug was fixed by Apple, so you do not need to do anything. If you are still having this issue, please leave a comment here.
It seems that many users are still having this problem.
- Reset network settings (General->Reset->Reset Network Settings)
- Toggle Airplane Mode on/off
- Restart your device
- Turn off Cellular Data ( Settings > General > Cellular) then try to connect to your WiFi.