Cost
In general, phone service via VoIP costs less than equivalent service from traditional sources. Some cost savings are due to using a single network to carry voice and data, especially where users have existing under-utilized network capacity they can use for a digital phone at no additional cost.

Functionality
VoIP technology makes easy some things that are difficult with traditional phone networks:

• Incoming phone calls can be automatically routed to your digital phone, irrespective of where you are connected to the network. Take your digital phone with you on a trip, and anywhere you connect it to the Internet, you can receive your incoming calls.
• Call center agents using digital phones can work from anywhere with a sufficiently fast Internet connection.
• Digital phones can integrate with other services available over the Internet, including video conversation, message or data file exchange in parallel with the conversation, audio conferencing, managing address books and passing information about whether others (e.g. friends or colleagues) are available online to interested parties.