Wifi button is greyed out

http://support.apple.com/kb/TS1559

If this doesn't work:

http://support.apple.com/kb/TS1559

...save yourself the hours of googling, resetting, rebooting, restoring and just bring it in. It seems to be a common issue. If you are in-warranty they'll likely replace it.

Unfortunately Apple does not understand that their phones came out with a hardware problem. I had a chat with a support representative and after sending me the same article which supposedly solved the issue and after I told him a zillion times that it didn't work, he finally said that my phone needed "service" ... Does this mean that they'll repair it instead of replacing it? ... I do not know. The truth is that it seems that support for this kind of issues is unavailable overseas as I live outside the US at the moment and the Apple representative could not help me with this. So in short I spent almost 600 dollars in a damaged "Unlocked" iPhone 4S which has no support outside the US. Very disappointed with Apple. Bad products being released out to the market and useless support service. I think I'll go with Samsung.

Seems silly but turn off phone then heat the back pannel of phone for a couple of mins, with a hairdryer for example. then turn back on. Worked for me.