Some times you are in a area where 3G signal is weak and your phone may constantly jump between 2G and 3G mode. It would be really annoying to browse or stream video in that situation.
Some OEM like Samsung provide a way to use 2G/3G only mode from their settings menu. But most OEM don’t.
Here is a way to access the hidden menu in all Android devices regardless of OEM.
Open the default dialer and enter the following code.
How to (video toturial)