In general, a telephone service via VoIP costs less than an equivalent service from traditional providers. There are also some cost savings due to using a single network to carry voice and data. This is especially true when businesses have an existing, under-utilised network capacity that they can use for VoIP without any additional costs.
The rigid nature of traditional telephone services makes some functionality hard or, sometimes, impossible to offer. For example, incoming phone calls are automatically routed to your VoIP phone whenever you plug it into any network with internet access. You can take your VoIP phone with you on a trip and, wherever you connect it to the internet, you can receive and make calls.
People are probably already making VoIP calls from their standard phones without realising. Communication companies use VoIP to streamline their analogue networks.By converting analogue signals into digital ones and back again, they seriously reduce the infrastructure required, especially for long-distance and international calls. As the infrastructure goes digital, VoIP will overtake analogue as the most popular form of voice communication.