Jailbroken iPhone Unable to Join or Connect to Wifi Network

Many guides say to reset all your network settings but you can go to Settings>Wifi then tap the blue arrow next to your network, then 'Forget This Network' and then try re-selecting it. It should ask for your password, which is the WPA/WEP key you set for your network, NOT the password to the router.

It might take a try or two but it seems to eventually work. I just did it again and it joined on the first try with a good connection.

Tested on a 2G iPhone with 3.1.3 firmware and the baseband unlock.

A pain, but the benefits of jailbreaking are many.