I have done about 8 hours research on this problem. Very rarely does anybody talk about the software component of this issue. So frustrating. You can go to the fix at the bottom if you get bored
***The problem. Wifi is Greyed out (Wifi is Grayed out) It will come back on intermittently / at random and then drop out for long periods.
1/ It would seem if I put it in front of a heater, into the freezer it would work for a short period of time. (Thinking it was the chip solder problem)
2/ I found if I turned off WIFI, Cellular data, blue tooth, and put it into air-plane mode (you have to do all these things for the experiment to work and the stack to be rebuilt temporarily) Then fully turn the phone off (power it down) Wait a sec and then turn it back on. Then you can turn your data services back on. If you find that your wifi comes back on temporarily you may very well have a driver service interruption problem. The wifi/blue chip driver will restart ok but another service will start and cause a over flow problem.
***Explanation of how I found the problem
Anyhow I was frustrated that apple did not have a way of sending sms like the Samsung Kies software does. I went to the Apple store and installed quite a few programs that promised this functionality. None of them did.
So I uninstalled them all. A couple of days later when I rebooted my phone after a while the Wifi stopped working and would not connect. I then turned Wifi off and tried to turn it back on but it wouldn't. It just became Greyed out. That is where my problems started. (I didn't realise the 2 issues were related)
After reading allot via mr Google I decided to reinstall my system via Itunes. I updated to the latest version of Itunes. (iTunes 11.0.4 for Windows (64-bit)
I did a restore from back up. (no luck (read no fix)
Looked at the update version (it wanted me to update to 6.1.3) (no go as I have read many people do this but the problem comes back after a couple of days to a week - so this possibly was not the solution (wanted to keep it up my sleeve)
******Back the **** up people and make sure the backup works*****
I then Jailbroke my phone via Evasion. Installed Ilux RAT via cydia and used option 12. (please note option 1 will not fix your problem)***Read the instructions*** and it worked. WARNING THIS WILL WIPE YOUR PHONE AND TAKE IT BACK TO VIRGIN JAILBROKEN STATE*** My wifi worked perfectly. I then installed my back up from Itunes to my phone. All is perfect in the world.
A few days ago I spoke to a apple tech that explained to me that it is now a well known problem. It is a issue with a large batch of chips. It seems that the chip has some sort of a built in expiry date. He could not expound on the issue or comment further. I asked him if updating the software had anything to do with the issue. He replied that he could not comment on the fact that the update to any software triggers the issue. A interesting choice of words and a answer in itself. It is good that Apple is finally taking hold of this problem. I did not have to pay a cent to swap my 16 month old (4 months out of warranty) Iphone 4S (64 gig) Interestingly in over a year the battery had reached the end of its life cycle as well according to the instore test the tech did. My other 4S that I have for personal use and bought in the same week from a different store does not have this problem. With a new phone came a new battery and os 6.1 (I was so glad it was not 6.1.3)
(no paying $200, No questions, so glad to have a phone that works again)
It seems all the trick above just reset the lease expiry date of the chip and let it work again for a little time till the lease is expired and the software shuts it down again)