The home screen uses for the internet connection the same destination as the web browser. When the destination group includes both Wireless LAN (WLAN) and packet data access point (cellular network), the connection is established with the first one that is available. Typically the WLAN access point is placed first in the destination group list and the connection is established via WLAN if the phone is under WLAN coverage.
Select Menu > Settings > Connectivity > Destinations to create a destination group which contains the WLAN access point.
If the phone is already connected via cellular network (3G/GPRS) when entering WLAN coverage, the home screen connection can be switched to WLAN by long-pressing END key to disconnect the current internet connection. The phone will then reconnect via WLAN if the WLAN network can be found and the WLAN access point is the highest priority access point in the destination group.
An alternative way to disconnect the cellular network connection and force a reconnection via WLAN is to select Menu > Settings > Connectivity > Connection mgr. > Options > Disconnect.