Right. Well I know I'm beating a pretty dead horse (probably dismembered from the beatings its taken thus far) but I'll lob my hand up and state that my 4S' wi-fi has been unreliable [read: a complete nightmare!] and only since updating (pretty late) to 6.1.3.
I must admit, I updated blindly in about May/June (normally recommended updates improve things and such) without consulting forums and consumer experience like I normally do. Wi-fi started to grey out around July, and restoring the phone would fix the issue for between 2-6 weeks ('fixed' it 3 times since its onset). This morning, however, on the day of iOS 7 (which I've been extremely eager to see since I saw its beta first hand on a friend's handset back in June [he's a dev, not a hacker]) it seems to have conked out for good. 2 restores did nothing, and I am left feeling a little miffed, given that the phone was bought in Feb 2012 and I am well and truly out of any warranty (I never extend warranties given that I'm pretty careful and generally pride myself on knowing how to fix pretty simple things that I do end up messing around with - didn't know the product itself would mercilessly conk out on me a few months after expiry).
Given that restoring the phone fixed the thing, I assumed software problems (never bothered messing around with temperature - RRoD experience has left me wary of temperature fixes) had caused the wi-fi problem, but now that the restore doesn't fix it...I haven't the faintest idea. The only thing I can say, based on my experience and that of considerable others, is that I am certain that upgrading 6.1.3 increases the liability of this problem, whatever the problem may be. To claim this to be untrue because it 'hasn't happened to all devices' is folly. Susceptibility does not equate to certainty, and the dismissal of the claim on poor grounds such as that leads me to believe anything that may follow up from that is equally untrustworthy...
Not every susceptible genotype will display a phenotype. Not every susceptible engine will explode. Not ever susceptible device will bust.
Now, I have no real and actual help to give, unfortunately, but I can offer a sole piece of advice:
Trying to fix it by restoring it might work. It doesn't hurt to try, and it gave me an extra few months of usage.
Now I'm left with some options:
Suck it up and run on 3G (unfortunately, my contract is limited to 1GB per month. I just have to be frugal till February I suppose). I'm a student and there's no way I'm shelling out for a new phone.
Third party repair job. No idea whether it'll work or not, but it's a relatively inexpensive gamble, and the problem is probably related to the 'antenna soldering foibles' that seem to be all the rage recently (but then why would restoring have worked previously?).
Apple OOW repair job. This doesn't appeal to me given that regardless of fixing my issues, I don't feel that Apple deserve my money for a problem that I genuinely don't believe I caused. I'll happily use my laptop over my phone to watch YouTube videos rather than shell out ยฃ200 to the people that screwed me when the problem is likely to manifest itself again. Call it stubborn, I really don't care. I call it principle.
...obviously I'm going to wait *and pray* that iOS 7 is my lord and saviour and that it was indeed a software issue. 2 more hours of hope. Who am I kidding? I'm not hopeful at all.
/story