I have Tmobile-US with no EDGE.
APN setting (under Settings -> General -> Network -> EDGE) used to be setup for "", and my Wifi was working after iPhone was checking that there is no EDGE, it was switching to WiFi and it was working OK. .

Now I don't know how, I have deleted the last number, it looks like that "192.168.1" and since all the way of the bottom of my screen does not work I can't put ".1" back (The ".123" button don't work.) , and iPhone does not switch to wiFi after not finding EDGE.
I have never changed the EDGE settings since I bought the iPhone(1 year ago).
There are also username and password for cingular.

My home router DHCP uses 192.168.10.x if it helps.
Interesting thing is, when I go to WiFi settings it still shows that it got connected to my home network, but the little Wifi Icon (next to cell phone network name on the main screen) never shows up.
Instead there is always "E" edge icon over there.
Whenever I want to do something on internet like "weather, you tube, safari" now it's giving me there is no EDGE error, instead of switching to wiFi.
Does anybody had the same issue? And please keep in mind, my bottom button does not work only on keyboard.