You have to call it an accessory, since you CAN make calls without it. But one of the most popular new VOIP accessories available for Residential VOIP networks is a VOIP-enabled phone. While you can use standard phones with most commercial Residential VOIP services and a special adaptor, VOIP phones plug directly into your computer through a USB connection. You can use these phones with compatible computer-based Residential VOIP service, like Skype, or even Google Talk or MSN or AOL Instant Messenger. Worth it? Depends on how much you use the service like a regular phone. If more than one person uses the VOIP service, it might make sense. Otherwise, you're probably better off with a headset.