Push Calling is a new phone calling method that works on mobile phone using VoIP technology. It involves receiving phone calls through a service even though you are not logged in to the service. Push Call is introduced by Telfree, a Swiss company providing VoIP services for mobile phones.
As a matter of example, you can receive a phone call on your mobile through TelFree even when you are not logged in to the service and even if the softphone client is not running actively on your machine. Actually, the client works in the background and pops up whenever there is a call. When the call enters, you only get a message notification asking you to choose whether to take it, in which case, you log in and the application springs forward and goes ahead with the call.
Through Push Calling, you can also call a person who is not online. As long as they have their phone, they can choose to log in and answer. This is quite innovative, and has yet to be implemented with other more common mobile VoIP services.