well, as many people I had this issue after I upgrade the firmware to IOS 6. And after a long chat with apple's senior advisor I find the way to fix it.
If you had
*reset the network settings (settings/general/reset/reset network setings)
*restart the iphone (several times until it's not grayed out) (both bottons
*uninstall & reinstall iTunes
*put it on the fridge or hit the motherbord (this is crazy!)
*Wi-Fi or Bluetooth settings grayed out or dim (http://support.apple.com/kb/TS1559)
*Troubleshooting Wi-Fi networks and connections (http://support.apple.com/kb/TS1398)
*Restoring iOS software with iTunes (http://support.apple.com/kb/HT1414)
*How to back up (http://support.apple.com/kb/HT1766)
and still your iPhone doesnt get WiFi, is because is too late! it's a hardware problem (even if randomly sometimes it works)
Well, Check Now Your Warranty!!! Apple will fix it for free.
If you are out of warranty ;( as I am ): send it to fix, it can cost up to $199USD...
Now, some interesting info on my char with apple:
but can you agree on that this update cause the issue then?
I mean, before the update it was working perfectly.
Well I can agree that the hardware failure was revealed by the update. The software itself works just fine on many phones.
and now I can't reverse the software update
but it doesnt work fine on many phones too.
Once an issue has been revealed service is the method we have to resolve it. If we had some better option we would certainly offer that instead.
I think that if the issue appears after apple make it available & tell everyone to Update all your devices, apple should cover the issue that this software update reveal.
I mean, I imagine no one knew about this issue, but it's certainly not our fault to follow what apple says. If apple says update the IOS because the new one is better, I guess everyone do it! isnt?
Software updates are some of the larger changes you can make to a device as it updates the firmware as well as the software. If the firmware fails as a part of that update we certainly cover it while in the warranty but if the hardware fails out of the warranty it is unfortunate that it would need a paid repair at that point.
There have been situations where if it affects a lot of people we do offer service out of the warranty. We publish those as repair extensions on our web site http://www.apple.com/support/exchange_repair/
(we are not there)
so, Please click on "I have this question too" so we know How many people have this WiFi issue.
let me know if you find some other way to fix it!