This is like a central office in a box. it's a complete unit that provides telephone service to your house through the internet so it uses VoIP. It has a built-in ringing generator that will ring any telephone that's hooked to it. so for example, if you wanted to say hook up a base handset that has four telephones or handsets connected to it then when you call the Ooma number it would ring all five units in the house. making this very convenient. when activating the number you can select your area code or even port an old number to it.