Enable only Wifi Internet on HTC Windows Mobile

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