TS1398: iOS: Troubleshooting Wi-Fi networks and connectionsLearn about iOS: Troubleshooting Wi-Fi networks and connections
In colombia there are iphone with this problem, disabled wifi and no warranty. Happens to these errors??? What is happening with apple???
See this: http://support.apple.com/kb/TS1559
If you carefully follow all of the steps in the above technical support article and none of them resolve it your phone is broken. You will have to get it replaced.
I had the same problem. WiFi option had greyed out and no matter how many resets, never worked. I had pretty much given up but the latest update to 6.1.3 seems to have fixed it. Just out of the blue. Its been more than a day now, and its still working great. Fingers crossed.