How can I set Android Galaxy Ace to only use 3G network?
I was in trouble getting my 3G to work, and I did these steps, that solved my problem:


Go to the dialer and type *#*#4636#*#*
Tap "Phone info"
Scroll down, you will see GSM selected;
Open the list and select WCDMA only;
Turn the radio off and turn it on again (there's a button for that on the screen)
Press Home Button, not back button


If you still can't get 3G, reboot your phone and that's it ;)

Enjoy! :)