Further details on the fine print from an engadget.com story:
"Even though you can all over Europe, Asia, and the Americas (to 60 countries and counting), if you want your pals to call you on Gizmo from their landlines, you're going to have to buy a Call In number. (Fret not though, since those cost as little as $3 a month.) Also, in order to call them up they need to have a number registered to an active Gizmo account, which increases the barrier to entry by a bit."
Still, it makes you wonder about the business model that they have in mind.