Imo, it just depends upon the guild members and their preference, there are guilds that prefer ingame chats and there are also guild that prefer other chat facilities, this could be due to several reasons such as server bieng full, downtime etc.
I find outer chat services better cuz it's the only way to chat eachother during a downtime or long update. Theres a plus point i find in using outer chat services which is sharing pictures/music/videos.
The channels and services are cool,i just hope for some secondary rank and more cap in guilds.
Thanks.