I remember using teamspeak in the EARLY days of my pro gaming days, and later we changed to ventrilo. Some of the guys complained that ventrilo took up so much more resources (*cough* I was one of them too *cough*) compared to teamspeak, but that was the days of Storm's poor machine days.
We actually used our team leader's company's empty server as the hosting place for both teamspeak and ventrilo, until we decided to get a server in the central region (think we had one near Chicago), so that the game map hosting and voice communication had same lag for all people, including team members of our own and the opposition for fair gaming.