I use Vonage, and have used it since before they had money to advertise with. I recently went looking at other services, but none had what I was looking for. I have certain telemarketors that call all the time and I wanted to block them. Nobody has this.
So I ended up running the phone line from the voip box, to the computer, then to the house line. I have a voice modem on that computer. Then I have a program that monitors incoming calls and blocks flagged numbers and gives them the old "you have reached a number that has been disconnected ..." message as soon as callerID reports the incoming number. Then unavailable, anonymous, and out of area calls are put straight thru to voicemail. All other numbers ring my house phones and cell phones.