I have an iPhone 3G 16GB with 4.0.2 and my wifi is not working, I tried to fix it with reset network settings and other quick fixes like that but nothing. Sometimes it sees wifi networks but I can't connect. I don't think is a hardware problem because I can see the wifi mac address on the device.
Version: 4.0.2 (8A400) (jailbreak with redsnow)
Modem Firmware: 05.13.04
PS: On 3.1.2 the same thing. (jailbreak with blackrain)
Downgraded at 3.1.2, again...still nothing (jailbreak with redsnow)