Skype costs money, man.
We do have a few Ventrilo servers among us. I briefly had a Mumble one on the same account I have our TF2 server, but I converted it into a Vent server. Mumble doesn't have a lot of the annoying problems Vent does, but it has a lot of its own.
Profanity has a Vent server. It was our original World of Warcraft server.
Krud has one as well, which is the current Vent server we use for WoW and whatever else.
As for the one I have, I just got it to test Vent out from the same location the TF2 server is located, since its latency is usually great. Wasn't so much expecting to keep the server.