When I was playing Alteil in Japanese server, the chat system seemed to be used for "guild meetings" a lot.
You log in the game, make a chatroom for your guild, and just check it every now and then and see if other guild members enter your chatroom. (You can see if your friends are online or not in the main tab)
I've started seeing chatrooms named after their guild on our server too. And I think it's a great idea to communicate with your guild member. (and exchange the info about other users' strategy and such...)
I guess we just have to keep reminding everyone that the chatroom is there!