If I enable wifi, and 3g is not available, will the di automatically find an open wifi and switch to it or do I need to find an open wifi and select it?
For one, WiFi is generally much faster than 3g as long as you have a good WiFi signal.
Edit: You have to tell the phone to us a WiFi hotspot the 1st time you connect to it. After the first time, if the hotspot is in range, your phone will auto connect to it (as long as you have WiFi turned on of course).