The reason I say good fit is that its free. And it comes in Linux/Windows/Mac versions.
As for the server side... Ive run full ISP servers for about as long as Internet has been Internet. But the problem I have with Mumble is that I dont see an option to run it in text mode. I dont like bogging down my server with gui menus. On the other hand, Ive preached often that anyone can run a server. Any computer in the closet because it wont run the latest windows games can run free software and be more internet server than you and a 100 friends would ever use up. Unlimited email, unlimited webpage space, and running online worlds or games.
http://www.dom3minions.com/ServerInfo.htm
I do agree however that IRC is a better answer. I might consider running an IRC host on my server just for CoE3 altho I wouldnt have to since there are so many free IRC servers already available. I might even pick one and homestead a #CoE3 channel. And of course HERE the Chat button on these Shrapnel forums will still work for it without anyone having to download any software.