Seeing all the comments, I think the best option could have been 2G default off (perhaps with a popup when nothing but 2G is available saying that "fallback to

Seeing all the comments, I think the best option could have been 2G default off (perhaps with a popup when nothing but 2G is available saying that "fallback to 2G temporarily? It is not encrypted" kind of alert, with the exception of emergency calls always available over 2G regardless of user prefs.