Ham radio. 300 baud packet over HF (thousands of miles) is still a thing, as are newer data modes such as PSK31 and the JT family. I'm actively working on 1200 baud projects over VHF FM now. Back in the day BBS was very much in. These days the same tech is more often used for telemetry, tracking etc (APRS). Now you can do it all in software, ref https://github.com/wb2osz/direwolf and friends.