First there was Mint Telecom that allows calls to be made from one number to a designaed number for less by moving the call from your cell phone over to a VOIP network then dumping the call back to the PSTN.
Then PhoneGnome's David Beckemeyer created MobileGnome which lets you set up a call from our cell phone's data connectivity using a small XML application
Now along comes Talkety, a web browser based suped up call out/call back service that uses a web interface to pair up calls making both legs of the call an inbound call.
The benefit here is with the International market where the Calling Party Pays so the calls end up being less than if dialed from a regular cell phone. Now with an EDGE or UMTS phone that's always on, an in country data plan means savings on voice minutes....Interesting.
Note: As Aswath asks this is not too different from JaJah until you read the fine print. The company allows free Talkety calls between users on the same network, but for now only in Germany.