Doing a VoIP phone roundup is a little trickier than you might expect. Most VoIP systems are now based on SIP (Session Initiation Protocol), in many ways the successor to the H.323 protocol that really kicked off the VoIP movement. Doing a VoIP phone roundup is a little trickier than you might expect. Most VoIP systems are now based on SIP (Session Initiation Protocol), in many ways the successor to the H.323 protocol that really kicked off the VoIP movement. SIP was first devised as a draft spec in 1996 as a way to create, manage, and terminate online multimedia sessions, music in particular. As it evolved, though, SIP proved to be a handy medium for achieving some traditionally phone-like functions, such as establishing a user's location on the network and adding, dropping, and transferring participants from a call.

SIP is an IETF (Internet Engineering Task Force) standard. Unfortunately, though, the ways in which carriers can implement SIP are not standardized. Some carriers implement an "open," or cross-compatible, SIP architecture; others, such as Vonage and Skype, render their systems incompatible with other services. Moreover, just like with cell phones, carriers can key SIP-based devices to different carriers. I wanted, for example, to try out VTech's ip8100 5.8GHz cordless VoIP phone system, but it's tweaked to work only with Vonage. Some phones are keyed for Lingo, and so on.

Ultimately, I decided to aim for the broadest possible consumer VoIP platform that didn't necessarily tie me to a fee-based subscription service, and that meant Skype. To test, I snagged my trusty Sennheiser PC 160 Pro-Gaming headset, which was a bit overkill for VoIP but provided a good subjective benchmark. I also ponied up $ 20 for Skype-Out credit, letting me not only make Skype-to-Skype calls with a handful of guinea pigs around the country but also Skype-to-cellular and Skype-to-POTS (Plain Old Telephone Service) calls. Up front, I'll say that Skype-to-cellular sounds terrible. Even when the connection is ungarbled (odds of this seem about 50/50), fidelity is so poor that call participants are often only semi-intelligible. Skype-to-POTS calls are better, sounding more on par with conventional cell phone calls, only a bit more distant.

The fact is that while Skype-to-Skype is still prone to occasional disconnects and connections with hopelessly mangled line quality, most calls are solid and shockingly clear