The KaZaA folks are getting into the VoIP act with a new product called Skype. Unfortunately, in contrast to their SIP-based counterparts, Skype is apparently basing this new service on a proprietary closed system, and thereby users of the service will not benefit from interoperability; they will not be able to communicate over the Internet with users that are not also Skype subscribers.
Users on other VoIP services based on the SIP standard, such as Free World Dialup, IPtel.Org , and SIPphone.com , can all communicate with each other over the Internet, much like how users on one e-mail service can communicate with users on other e-mail services. Skype is not joining that community, however, so Skype users will only be able to communicate over the Internet with other Skype users.
