my iPhone 3G is not able to connect to any wifi network

Have you tried this article?

http://support.apple.com/kb/TS1398

Hi. I have same issue. I have a disabled iPhone 3G (Model A1241) and the WiFi does not pick up any networks. I even replaced the WiFi antena thinking that was the problem. I've restored it multiple times and still doesn't even pick up a network signal even though other ipads/iphones and computers do. I reset linksys modem and still nothing.

Have you tried to restore it as a new device then attempted to connect to wifi and not from a backup

I have the same problem, I'm using an old iPhone 3G, activated with original SIM, then I put my working SIM in and can connect to AT&T, but when I go to WiFI it does not detect any WiFi.

First thing is wifi grayed?

http://support.apple.com/kb/TS1559

If it is you should back up and restore as new hoping that is just the mac address (settings>general>about>Wifi Address) usually is composed by letters and numbers, if it's not restoring as new.

http://support.apple.com/kb/HT4137?viewlocale=en_US

Or if not just add your wifi as other (manually) and tap the password manually Settings>Wifi choose other, and so on...

Hi- Yes I tried manually adding the network (even deactivated password requirements on my home network but still doesn't work.)

I was reading another thread that has similar headline - seems the issue is with the upgrade to software iOS4 on a 3G. Folks have been able in some cases to get replacement phones. Seems issue is isolated to XP version. I have a MAC at home, so I will try to restore (yet again) on that computer and see if I can use it, otherwise I guess I'll go plead my case at the Genius Bar 🙂

Thanks on the responses. See "Wifi not working after updating to OS4 on iphone 3g" for more specifics.