Most android device come without a separate option for 3G. That is, the 3G is automatic, it only enters when the signal is high.
but most times you might want to force it on
the phone maybe because of a slow download and probably because you hate
wasting time when you know your internet speed can be improved.
To do this, all you have to do is
Root your device
Download and install superuser
install busy box
and install PIMP MY ROM
Grant pimp my rom, super user right
1.Open pimp my rom
2.Click on Tools
3.Select DEVICE HIDDEN MENU
4.Click on ACCESS HIDDEN MENU
5.Select PHONE INFO and at the bottom is
option for WCDMA.
6.Select WCDMA ONLY and exit PIMP MY ROM.