No one wants to host a Team speak or Ventrilo server all the time
and for some people Skype can really lag up a game
but here is the easiest (but apparently not the very obvious) solution
Download steam it's free (if you don't already have it) -
http://www.steampowered.com/Make an account
Start a party chat (start a chat with a Blockland friend and invite others)
Then in your server, set the welcome message to something like this
"Hello, we are currently in a steam party to use voice chat, please add (steam name here) and join!"
Now the reason I'm saying use steam, is because it's a bit easier to use for most newer users
not only that, but because it uses less processing power than Skype, and won't lag up your game (as much)
I hope this was helpful