In my Android game I have a turn-based multiplayer. Users wait for opponents in the lobby and whenever exactly 3 are matched, they go to a new game room together, which is a
So, one of the reasons we wrote all the Google Play game services samples as single-Activity games is because switching between Activities require you to disconnect from the GamesClient and connect a new one from the new Activity.
So using Fragments is probably the easiest way to go about this. It's also pretty clean and allows you to make a tablet layout by combining them if you want to.
In particular, if you are setting up a multiplayer game, disconnecting will disconnect you from the room, so you can't switch to a different Activity after starting the handshake :-)