It all started sometime in 1990.
Here's a Telix log file that Steve Deppe archived from 1990, showing that Steve downloaded (at 2400bps!) this “new bbs” source code that Rob started developing (in Turbo C) in November of 1990:
90-11-27 23:21:34 Telix Usage Log Opened. 90-11-27 23:22:16 Connected with : RS line 1 sys dnet 90-11-27 23:22:16 ++ At phone # : 1 714 529-9525 90-11-27 23:22:16 ++ Settings : 2400,N,8,1 90-11-27 23:49:43 Download using Zmodem protocol. 90-11-27 23:49:44 ++ File : I:\lib\newbbs.zip 90-11-27 23:49:52 ++ Chars per second : 192 90-11-27 23:54:35 Elapsed time online 00:32:19