Sharing.. from one of my Colleague...

Hi Guys,

This is news to me, and scary news at that, but it seems as though firmware update 2.2.1 has been causing some problems with Wi-Fi for many iPhone users.

If you have been having issues, and were hoping for a quick software fix, it looks like you may be out of luck.

Some users have reportedly been told by Apple to have their hardware replaced, and to make sure that when they call for a replacement, they specifically ask for an iPhone that’s running firmware of a version earlier than 2.2.1. All of which would seem to indicate that for the moment, Apple doesn’t know how to undo what they did with 2.2.1.

Your only solution will be to wait for OS3.0 and update your FW then. At least for now! Or keep your finger crossed that someone will find a fix for it
For more info... http://www.theregister.co.uk/2009/04/08/iphone_wifi_again/

Cheers...