If you want to dive into the world of Internet telephony but prefer to use your existing phone—not VoIP software on your Mac —as your primary calling device, you might consider subscribing to an Internet telephony service provider (ITSP). An ITSP uses your broadband Internet connection to deliver telephone service to your home or office, usually at a steeply discounted rate. Unlike desktop VoIP tools, ITSPs don’t require that you use your computer to place and receive calls.