VoIP phone services let you replace your traditional landline phone with one that connects over the Internet. Today, your phone works on what is called the Public Switched Telephone Network (PSTN), a private network that reaches into your home through the standard phone jacks in the wall.
With VoIP services, your phone connects to the Internet over your cable or DSL modem. To do this, VoIP service providers bundle a small device, called a telephony adapter, that plugs into the broadband modem and translates the electrical pulses from your phone into IP packets that travel over the Internet. The way you use your phone is the same, even though the network underneath changes.