It happened to me after I updated to AT&T GB early Feb 2012 and rooted the phone using the method for the Canadian version of Infuse. I lost wifi completely. Check out this thread: http://forums.androidcentral.com/in...s/160053-rooting-infuse-t-gb.html#post1646026
I actually sent my phone back to Samsung and they put back the stock Froyo on it. If you follow that thread, there was a suggestion by tamelion which seemed reasonable that you can try.