Don't buy any Apple products - none represent reasonable value for money.
And if you must buy one, don't ever update/upgrade software because Apple do program their IOS to kill off old devices batch by batch - this explains why some people experience the No WIFI problem while the rest seem to be okay. And the fact is Apple will never allow you to downgrade IOS says it all.
For the unlucky one who can't fix their problem by resetting and all other software tricks, try FREEZING because Apple program their phone to shut off the Wifi once the Wifi chip is a little hot, and try Hair Dryer blowing if the freezing only return you so much much time before you need to refreeze again.
Why hair drying ? Because WIFI chips in certain batches are not printed/soldered properly (defective) and therefore when the new IOS runs, there is a bottleneck of current unable to pass through smoothly, and causing the chip to overheat as a result. Apply heat to the chip area (on the other side of the camera, just below the headphone jack hole) will help to somewhat to allow more flow to the demanding IOS 6 especially IOS 7 (which is designed with lots bullsh*t running in the background - that's what eat up your battery too).
Unless Apple is willing to change IOS and make it compatible with older phones, the only solution is to downgrade IOS back to IOS 5 which they refuse ... meaning they want you to keep buying new phones.
If you want to use Apple products, be ready to keep buying new gear or your best bet is NEVER update software.
I welcome Apple to to tell me this is not the case.