Someone has said “Going from iPad 1 to iPad 2 is like going from dial-up to broadband.”
Here is the dial-up modem, USRobotics Sportster Voice 56K Serial interface External Modem.
Before the popularity of digital broadband, home users had to buy either an internal or external dial-up modem and made it connecting between the computer and the analog telephone socket. For those playing BBS or early days of Internet in late 1980s/early 1990s, modem was nearly the only choice for normal home users connecting to the outside world.
This modem comes with a standard serial interface connector. The serial interface (also known as RS-232), along parallel port which was commonly used to connect to printer, were the most common ports found in PC connecting to external devices. Nowadays, these two types of ports have been replaced by USB ports although serial interface is still the standard for many industrial or commercial electronic devices.