I'd say a chat group is absolutely needed @Andypandy87 being a leader of one alliance previously, and an officer in others, I dont think an alliance can communicate effectively and achieve results without something extra.... the ingame chat just doesn't cut it.
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I prefer Line over any other apps.
I also have a chats just for the following:
Officers
Each AQ BG
Each AW BG (if they are separate from AQ)
I use Line in my ally.