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, but it is necessary to have internet access to originate the call.
One can also sign up for the service for free and a certain credit will be automatically given. Registered users also enjoy Free Global Calling.
JAJAH Free Global Calling allows you to make free local and international phone calls. It applies to land line and mobile calls to and within: the United States, Canada, China, Hong Kong and Singapore; and it applies to landline calls to and within Australia, New Zealand, Taiwan, the UK, Germany, France, Italy and most other European nations.
It applies when both call participants are registered and active JAJAH users. In countries where free phone calls are not available, or if someone is calling a non-JAJAH member, calls are subject to JAJAH’s regular low rates.
The free service depends on users paying for other Jajah services and it depends on people using JAJAH in a “fair and reasonable” way. Of course, there are several conditions for the call to be free (Read this page). Another point to take note is that Jajah is giving free calls for any registered user to any landlines in the world on 25 Dec 2006. So I realised that one way to 'make active' your account for 2 weeks will be to use register and call someone on Christmas day for free.
Anyway some clarifications (on how Jajah works) from the forums:
Technically speaking, when you initiate a call through JAJAH, from the phone company's perspective it is like you are accepting an incoming call. Normally phone companies do not charge for incoming calls, but if you normally pay for incoming calls, the same will apply with JAJAH. The payment for the calls initiated by JAJAH is done separately from your regular phone bill directly to JAJAH.
Also if you are outside your mobile provider’s coverage, certain fees, called “roaming fees” will apply. This additional charge is by your cellular carrier and it is paid to him, and not to JAJAH
The one BIG advantage of Jajah to other VoIP services like Skype is that it would be possible to use it even with a slow dial-up connection (which is too slow for voip).
See also: Interview with Roman Scharf, CEO of Jajah