More than 30 years ago Internet didn't exist. Interactive communications were only made by telephone at PSTN line cost. Today we can see a real revolution in communication world: everybody begins to use PCs and Internet for job and free time to communicate each other, to exchange data (like images, sounds, documents) and, sometimes, to talk each other using applications like Netmeeting or Internet Phone. It starts to diffuse a common idea that could be the future and that can allow real-time vocal communication: VoIP