Phreakmonkey YouTubed his vintage Livermore Data Systems "Model A" Acoustic Coupler Modem connecting to a modern Linux box. At 300 baud. That's about 30 characters per second.

He says, "This modem was given to me around 1989 by the widow of a retired IBM engineer. Even better than seeing it in a museum, I decide to hook the trusty Model A up and make it talk to something. After some trial and error, I manage to get it to talk to a terminal server at work and use it to connect to a linux box. It's ALIVE! So, 45 years after it's creation, this antique modem gets to send data to and from the modern Internet."

1964 Antique MODEM Live Demo [thanks, Matrix!]