App to toggle 2G and 3G
Nope and I quite sure that something like this cannot be changed by an app, even if there was a toggle in the Settings.

Maybe there are solution provided the iPhone is jailbroken.



For the record, let me mention that the existence of such a toggle seems to depend on the carrier one use.

Reason for saying that is because I used to have the 3G toggle, but it disappeared after I applied a "carrier update" that showed up. Maybe in order to have the 4G toggle appearing? I don't know.

To avoid confusion, carrier updates have nothing to do with iOS updates