A:Answer There are two types, the single outlet where it sits between the wall and the phone, to filter out the internet signals and double outlet where it is used to separate the combined phone/internet signal from your service provider into two separate signal wires - one to your DSL modem and the other to you hardwired phone or base station of the telephone system.
You can buy them nearly anywhere and easily online, but are usually provided from the DSL provider if you got their modem. Cost is just a few dollars each.