Originally Posted by hrbuckley
Does the Wi-Fi icon turn white? If it does your Blackberry data will flow via Wi-Fi. The cell phone radio (3G) will stay on unless you turn it off.
...and if you turn off 3G you won't receive any phone calls, etc. So just like 'hrbuckley' said, once your device detects a network in the saved WiFi list, it will automatically connect (if you have it set on automatic) and the device will use your home network instead of 3G.