JaJah is an emerging "dial-around" service. From your computer, you tell it who you want to call, and it dials your phone, then the other party, and connects you to each other. The advantage of using a dial-around product like this: cost. JaJah charges 3 cents a minute for international calls.
The iPhone's strong Web browser should make it a great platform for JaJah, and JaJah just created a special iPhone version of its site, FreeYouriPhone.com. You use the slick interface and big screen to initiate a call, then wait a second for the iPhone to ring you before it connects to the other side.
Unfortunately, this is an instance where the iPhone's browser-only model for third-party applications fails us. The Safari browser does not, apparently, have access to the iPhone's contact list (or calendar). That's a good thing from a security perspective--you wouldn't want any old random site reading your iPhone's internal directory--but it stinks for communications services like JaJah. Who wants to have to enter phone numbers again into an iPhone that already has them stored?
Also, in my testing, the JaJah iPhone site wasn't quite cooked. The interface took up a tiny portion of the iPhone's screen, and was unreadable without a lot of two-finger zooming. That's fixable, of course. But the deeper integration issue may not be.