This is the Atari XM 301 300-baud modem, which I connected to my Atari 130 XE 8-bit computer to access local bulletin board systems over the phone lines. This was surfing in the late 1980s to the early 1990s: you dialled a local number (unless of course you were willing to pay long distance charges to access a non-local BBS) and waited for your turn to connect. If one other person was on the BBS you wanted, you'd get a busy signal. Sometimes it took hours to connect, all for a few rooms of text-only ASCII-glory delayed conversation with fellow geeks. Good times.
I could read the text faster than this modem could transmit it through my computer. Upgrading to a 1200 baud modem midway through university made surfing much more pleasant, though still nothing like we enjoy today.