https://play.google.com/store/apps/details?id=jp.naver.line.android&hl=en
It's a good messaging app, we have all members in a room together to talk, it's much better than the in-game chat.
When you leave an alliance, you have to wait 24 hours before joining another alliance, during which you won't have access to the alliance bonuses. Your new alliance's bonuses take effect immediately upon joining.