Calling from Gizmo to Gizmo is free, Gizmo to a real number starts at 1.8¢, more expensive than Skype, I believe. Getting a landline number for Gizmo is $5 a month.
Gizmo also supports Access Numbers: these being a list of number that real-lined users can call, then dial another identification number to reach your Gizmo account. Hm, does Skype support this..? There is FREE VOICEMAIL~ props.
Here's a post comparing Gizmo to Skype. http://www.randomthink.net/archives/2005/07/08/skype-vs-gizmo-project/
And now, the main reason why I mentioned, and noted Gizmo? Voiceposting. Now via your computer, by calling ljvoicepost on Gizmo. Granted, you'd need to be able to phonepost in the first place, but hey, I may use it more often now. Maybe. Maybe not. Quickass audio recording~ XD
Info via LJ's paidmembers community.