You cannot turn off 3G. If you loose the LTE signal the phone falls back to 3G otherwise you would have no cell reception at all if you were able to turn 3G off. Not sure even if the phones can fall back to pre-3G.
You are correct, you can't manually turn off 3G. Yes many phones will still fall back to 1X if there is no 3G signal.
You could set the phone to connect to a wi-fi signal, this action will turn off 3G.
To the OP, what kind of phone do you have and why do you want to turn off 3G?
Curious, how does connecting to WiFi turn off 3G? My 822 still connects to 3G when I'm home and the phone connects to my WiFi.
Well how else is the data going to go over wi-fi instead of mobile if you have both on?
Yes, true data via 3G is disable in favor of WiFi but you still have a 3G connection for calls and SMS. 3G isn't completely disabled with connected to WiFi, as per dirbon connecting to WiFi turns off 3G....