http://iptop.net/eng/faq.html
That will give some quick answers to basic questions about the subject

Put simply the telephone calls on the internet are the soundwaves of your voice broken up into packets of data and sent out via a connection-less communication using the UDP protocol. The reason for this is because of the amount of traffic that would be required to validate all the data being transmitted, our brains fill in the small gaps in the sounds that we hear from the transmission (which are created from lost packets)