This question has 2 answers that I can see.
The first one would be a Dial Up Modem. These devices allow (or allowed, since they're pretty much obsolete) a computer to communicate over the phone lines and access the internet.
The second option for an answer would be a DSL Modem/Router. In a sense, a DSL (Standing for Digital Service Line) is a bit of a predecessor to traditional Dial Up, using a digital telephone line (However not the frequencies used for voice) to connect a computer or set of computers together and to the internet.
