Are you doubtful that it is possible?
Well, you don’t need to be an hacker or a computer geek, but simply you need a cellular phone, a free Wi-Fi network and an application called fring.
In the video below is shown how this is possible thanks to fring, an application that uses your mobile internet connection to make peer-to-peer VoIP calls.
By using a Wi-Fi network connected to internet it isn’t even necessary a sim card!
A good idea to use your home or office wireless network for an unusual way to make and receive calls with your mobile device.
Furthermore you can use this system also in airports, hotels and all places that offer you a free hotspot.
Oh, I nearly forgot that fring works over 3G, GPRS and Wi-Fi networks and dynamically adapts itself to the optimal network !

Marketing VoIP Services To Non-Technical Consumers
Not All Consumers Understand VoIP
But you do not HAVE to make them fully understand the technology in order to get them to interested enough to purchase your VoIP service. You do, however, have to give them enough information and understanding of Voice over IP in order for them to be confident in making a buying decision. Here are some tips you can use, as a VoIP Service Provider, to help bolster your marketing efforts in order to increase your subscriber base.
VoIP Service Provider Marketing Tips
While it is one thing to identify points that VoIP service providers need to market to, it is another thing to execute on them. Execution, after all, is just as important as strategy. These points are merely a starting point for enhancing the marketing of your VoIP service – do with them what you will.