switching to GPRS when WI-FI is already on

[richardyu301]

When I am already on Wi-Fi, my X51v still tries to connect GPRS when I use the browser. Below is a link showing similar issue for HTC PDA Phone.
http://www.htcwizardweb.net/node/1235#comment-2429

I hv followed the advice and do below settings:
START > SETTINGS > CONNECTIONS > CONNECTIONS > ADVANCED > SELECT NETWORKS
- Programs that automatically connect to internet ..... "My ISP" (or whatever your ISP settings are called.
- Programs that automatically connect to private network ... "My Work Network"

However, it still tries to connect GPRS. it seems that something has be set up at Setting->Connections->Network Cards.... Unfortunately the article is for a htc PDA phone instead of X51v. Can any X51v user give me some advice on how to set it?