Hello everyone,
Hard to believe I FOUND THE SOLOUTION FOR greyed wifi. This is the whole story....
I am one of the dissapointed apple users. My iphone 4s worked flawesly. One day I decided to update to ios 6.1.3 and wifi started to causing me headaches. It didn't keep the wifi signal and when I was doing a fresh install the wifi button was going grey. My suspicions for software failure became stronger when I finally updated to ios 7 and then I lost comlpetelly wifi and also - new one - the bluetooth.
After several months of searching in google I found out a solution that I couldn't believe but I was so desperate that I would try anything. The solution was to put the phone in the freezer inside a zip bag for 20 minutes and the problem will be fixed for a while. AND YES IT DID!!! I couldn't believe in my eyes that my wifi and bluetooth were working until the temperaure of the phone return to room temperature. Through further search I discovered that the problem is at the chip of wifi (which includes the bluetooth). The contacts of the chip due to unknown reasons, loose steady contact so that any change at the temperature of the phone affects wifi. So there are two solutions. One is to go to an expert and replace wifi chip ($150) or take your own risk and reflow the wifi chip yourself. I took the risk and did it myself. I used a hair dryer pointing at wifi chip (next to camera at the back - search youtube) with maximum heat and air flow for 5 minutes. I let the phone cool down and after that my wifi is working perfectly at least the last 10 days I am using it!!!
My advise is to try first the freezer and if your problem is temporarly fixed move to next step.
Watch youtube videos and keep the times they are advising especially if you decide to reflow the wifi chip
I am not planning to keep my iphone for any longer. I will sell it to a fanatic apple user since I am not any longer.
I hope this will help most of you. If someone needs further instructions feel free to ask