Ok so I just opened up an Apple id just to share my experience with greyed out wifi problem. I bought my new unlocked 4S less then 2 months ago, and suddenly it greyed out the wifi option. I updated it to ios 6.0.1 and still had the same problem. I tried EVERYTHING that was mentioned on this forum, including a 30 minute call to Apple support with no result. The Apple support guy made me do things that I did myself already, soft reset, hard reset, reset network settings etc. Then he said it is a hardware issue and I am entitled to a replacement. I didn't want to give in my $549 unlocked iphone which is less than 2 months old, for a replacement I don't even know if it's new, used or remanufactured. (In fact I asked the Apple rep and he clearly said the replacement is NOT gonna be a brand new one). I wanted to stick with my phone since I paid full unactivated price & have unlimited 4g internet.
When I was at work yesterday, I did a soft reset while my phone was being charged (connected to a PC), and miraculously it brought back the wifi. So far, it still has the wifi option as normal.
The problem existed for a total of 4 days. Now I really hope this never happens again! And yes, Apple should pay immediate attention to this issue...