Would you happen to have a modem available for use on both ends? I was going to attempt what you are trying until I read about building a simple "phone line simulator" to bring up the proper voltages to the modem, allowing an old 33.6 Global Village Teleport to talk to a generic Windows softmodem on a cheapo Acer laptop from 2007. Zterm works nicely with pretty much anything on Windows, allowing file transfers with relative ease.

This more or less explains everything: http://www.jagshouse.com/modem.html