Vonage rolled out their 9-3-3 service which is simply a verification of whether or not you've enabled 9-1-1 on your Vonage line. This way you don't have to dial 9-1-1 and see if the police/fire/ambulance show up at your door and then blame your 3-year old kid for dialing 911. Excerpt from the release announcing the news:
TeleCommunication Systems (TCS), a global leader in mission critical communications, today announced that Vonage, a leading provider of broadband phone service, is the first Voice-over Internet Protocol (VoIP) service provider to utilize TCS' recently introduced VoIP Verify™ service. Designed for mobility, VoIP Verify provides Vonage subscribers with a simple tool to determine the availability and extent of the individual's emergency services coverage from the caller's current registered location.
I recorded a 9-3-3 call from my home Vonage line to determine if I was 9-1-1 verified. Take a listen to the .mp3 file if interested.