Jajah

Jajah is a VoIP (Voice over IP) provider, founded by Austrians Roman Scharf and Daniel Mattes in 2005.[1] The Jajah headquarters are located in Mountain View, CA, USA, and Luxembourg. Jajah maintains a development centre in Israel.
Jajah's primary service, Jajah Web, takes an approach called web-activated telephony, using VoIP to connect traditional phones (landline or mobile). Calls are made without download or user-installed software, and in most cases at rates lower than those of traditional phone companies or even free of charge.

Jajah Web connects existing traditional landline or mobile phones with calls that are set up via Jajah's Web site. Callers type in their own number and their desired destination number in a Web form. The Jajah service first rings the caller. After the caller picks up the phone the destination number is then dialled and the connection is established.
Jajah claims that their service works with any standard web browser. It does not require a broadband connection, nor is it necessary to be online when using the service, but it is necessary to have internet access to originate the call.
Dial-up internet users without a second phone line must schedule their call to be placed a few minutes in the future in order to allow for the time required to disconnect from their ISP and free up the phone line.

Jajah Free Global Calling
Jajah launched a service offering free calls globally on 28th June 2006. The service is limited to specified geographic areas, and Jajah has also adopted a Fair Use Policy which limit the amount of free Jajah calls.
Calls between registered Jajah users are free of charge for landline and mobile calls within the USA, Canada, China, Singapore, Hong Kong, Thailand and apply also for landline calls to and within most European countries as well as Argentina, Australia, Israel, Japan, Malaysia, Mexico, New Zealand, Venezuela and Zambia.
A further limitation is that scheduled calls and conference calls cannot be free.(From Wikipedia)