The same thing happened to me 3 days ago and to many others as I can see from the other posts-complaints.
See if these solution helps you:
2) You can also try to open and close the airplane mode and then try to switch on again the wifi.
3) Press Power button and Home button at the same time for about 10 sec until the apple sigh appears, wait for the iphone to start operating again and then try to switch on the wifi
4) More tips found here https://discussions.apple.com/thread/4313031?start=300&tstart=0
All the above tips didn't help me but maybe you will be luckier
If not I can only imagine that is IOS 6.0.1. problem and I am waiting for an update bug fix cause I don't want to restore my iphone (this means that everything will be erased from my iphone and start from tha beggining)