start->settings->connections->connections
Mobtel Telenor Internet
My Work Network
Go to advanced->select My Wok Network [the first button over composition rules]
Here select "work" for everything.
Now, without 3G, the phone connects to internet only if you have an active wifi, otherways doesn't connect.
Source: http://softlabpro.blogspot.com/2010/08/enable-only-wifi-internet-on-htc.html
