A number of users continue to report broken WiFi under iPhone OS 2.2.1.
As described by one reader:
"I am having problem after 2.2.1 update where the iphone will only detect wifi networks for a moment, and then always go back to edge and no longer detect networks."
Enter DNS address Enter your routers configuration page on a laptop or another wireless-enabled computer (usually 192.168.1.1) and find the DNS address, then enter that address in the iPhone's Network settings pane.
Reset network settings Tap Settings, tap General, tap Reset, tap Reset Network Settings. This will cause your iPhone to restart, and will delete any stored Wi-Fi passwords as well as DNS settings and more. It can resolve signal strength issues in some cases.
Reseat your SIM card If your iPhone's SIM card is not seated properly, signal strength can suffer. Try re-seating the SIM by pushing a straightened paper clip into the small hole on the top of the device to open the SIM tray, making sure the SIM Card is properly in place, then re-inserting the SIM tray. Also check for debris inside the tray or SIM card slot.