Free Internet calling has always been plagued by a lack of interoperability. This was true of the startup companies of the 90's Internet bubble era or the more recent popular service Skype as well. The Gizmo project plans to change that with open standards and open networks.
Skype is based on proprietary technology which means that only users of the Skype software or phones can only make free Internet calls with other Skype users. Gizmo users can potentially make free calls to any system that decides to make use of the same open standards. Although Skype has a head start in terms of user base, this may quickly change.
Gizmo not only has open standards going for it. The free Gizmo software offers free voice mail and does not use your computer to route other calls as Skype does due to the P2P nature of the Skype service.
Just as with Skype, you can also call land-line and mobile phones with Gizmo for very low per-minute fee and receive calls to a regular telephone number by paying a small monthly fee.
The Gizmo Project is sponsored and managed by SIPhone, the VOIP service started by Micheal Robertson of MP3.com and Linspire (formerly Lindows) fame. One thing you have to give Micheal Robertson is credit for understanding the importance and potential of open standards and open software. Gizmo is a very cool product that will be giving Skype some very stiff competition.
Gizmo is currently available for Mac, Windows XP, and Windows 2000. A Linux version should be out soon.