I have used VoIP for almost a year now. A few weeks ago, I decided that I should probably hook it up to the house wiring so we could plug in a phone anywhere. My wife really isn't in a position to go running after a ringing phone at the moment. It worked great except you couldn't hang up.
I jumped on the net to figure out what I was doing wrong. Apparently, it is paramount to disconnect the telco from your home before hooking up your VoIP to the house wiring (which I didn't) as it could "blow up". Hrmmm - I disconnect the telco and no change. Hrmmm - these spliced wires don't look quite right. What happens if I .... bingo. One of the previous owners of the house had done a little of their own wiring and had created a circular loopback. Lesson learned - wife happy.