Raidcall is a nice free option if you're strapped for cash, I know they have issues with down time though so personally I wouldn't use them. Ventrillo I have never been a fan, it's outdated in my opinion. Teamspeak, David (I presume this ESO guild is linked to this site?) could link a self hosted teamspeak to his (if he has one) internet space thingy that he uses to host this site, if he does host this site him self. But then you can pick up a teamspeak host for 50+ people at like 10$ a month easily. I recommend Teamspeak, I've used it for years. If you want any recommendations on a host to go with, give me a shout