Wanted to share my experience, in case it might help anyone else.
I noticed a few days ago that my phone seemed slow when loading web pages. I checked wifi and sure enough, it wasn't connected. Now, I had recently connected to the wifi at work, but had disabled only that network, and realized finally that wifi had stopped working after that. When I went into the wifi screen, I got the spinning circle trying to find available networks, and it never stopped.
So, not knowing what the problem was, I thought perhaps upgrading to 6.1.3 would solve the problem (I had not upgraded to 6.1.2 because of the battery drainage issue and they had told us at work to wait). I upgraded, turned my phone on and the wifi was greyed out. WTH? After hours of research online, I realized two things: 1) my phone was 5.5 months out of warranty, and 2) I was 42 days away from an upgrade to iphone 5 for $99.
I tried every available fix to no avail. So I resorted to the hair dryer method. First time, it didn't work. The second time, maybe I got it too hot or something, I don't know. But I let it cool off for 2 hours before attempting to turn it on, and it froze up. I could not turn it on without doing a hard reset, or wake it up without having the apple icon appear and never go away. After a hard reset, I could swipe and get into the screen, but touching any of the icons froze the phone once again. Frustrating. I cannot say for sure what caused this problem, but none of the solutions I tried worked. I could live without the wifi, but I just wanted my phone to work at this point, to retrieve info if nothing else.
Once I got home, I had to unfreeze it first, then plug it into the USB on the PC to get itunes to recognize it (in the frozen state, itunes couldn't get a response ffrom it). After a back up, I restored it and thankfully it is working again. And amazingly, the wifi is working again. Perhaps the hair dryer worked, to what extent remains to be seen. But at least I am not out another $200 or even $600. I've learned my lesson - if the wifi quits working again (which is likely, after seeing all the comments), I will just wait until I can upgrade.