If you are on trip, you may to switch on airplane mode to avoid any roaming charge. But sometimes, when I was in a cafe with free Wifi, I turned the Wifi on again. Everything works really fine until I was back home. When I tried to connect my iPhone to my home wireless network, it didn’t work. As I checked out the Wifi option in “Settings” screen, the Wifi option is just grayed out or disable by iPhone itself. Even I rebooted the iPhone, the wifi option still stayed in disable state.
This is not the first time I heard from my readers or other jailbreak iPhone users about this Wifi problem. But, I’m also have same experienced it on my iPhone. And here is the fix:
Reset The Network Setting
Just resetting iPhone’s network setting, the Wifi option comes back to normal. To reset the network settings, go to “Settings” -> General -> Reset -> Reset Network Settings.
I’m not quite sure if this is the universal solution to the Wifi Grayed-out issue. But this one works for my case
iPhone School's Weblog 
hi i have a 2.2 2g iphone jailbroken and unlocked but i cant connect to a wifi network even after resetting network settings please help
Hi Iceman…
This is another solution from one of my reader (Paul- comment on 2009/03/02)…this may help you..
Solution, Fixed for Wifi Greyed out after jailbreak (Iphone 2G)
If your wifi connection problem is not due to AP settings (i.e. icon greyed out), I have tried various methods and found this to be the working solution to my case. I have used all jailbreak programs (quickpwn, winpwn, ziphone and others) and found the solution fix for Wifi. Would like to share so that the rest can spend their quality time on something more productive rather than going through what i have been through.
Despite the facts of some saying downgrade and upgrade of firmware, or using different version of itune to solve the wifi greyed out, it does not matter in this process.
I am on the following env when wifi is greyed out: Vista, Itune 8.0.2.2, Firmware 2.2.1 jailbreak. tried also on a corrupted restored and it works in both cases.
Solution to the problem:
– Use Itune to shift restore your firmware back to 2.0.2
– Use winpwn to create custom firmware on 2.0.2 (if you are on ATT sim), do not need to select unlock
– Shift restore iphone using the custom firmware created by winpwn
note: if you PC does not recognize iphone, first when iphone is detected as an unknown device, delete root hub one by one and vista will redetect one of them as mobile apple device. To do restore, switch off your phone, unplug USB cable, plug it in again while holding the home button for 20secs, vista will detect it as mobile device.
I am iphone 2G/2.2 user. I want to upgrade my version to 3 or later. Is it possible. Plz help.