Skype has introduced free calling within US and Canada. I am currently testing both Skype and Gizmo, even bought phone numbers from each service, so people with real phones can call me too
So far the testing shows that Gizmo still has plenty of space for improvement. Call quality is inconsistent – I got three calls from same land-line phone – all three were different in terms of quality, ranging from horrible to acceptable. Skype’s call quality usually just above that – ranging from acceptable to excellent. However, I haven’t done any tests over modem or cell phone connection (due in next couple of days).
P.S. Don’t forget a nice headset, it helps a great deal!