Today I found a tweak in my Android mobile to force load only 3G network. By default my network was loading in Edge even when the preferred network was set as 3G. There was no option to set as 3G only. 
Then I found this tweak from internet to force 3G network. Just dial ##4636## , then go to phone information. 
From there set it as WCDMA only under set preferred network type, after which the network mode changes to 3G. 