and non-AT&T models were also producing full-form modems to transmit data. Fast forward to the nineties and that speed grew exponentially from 300 bit/s to 56k, or 56kbit/s. In addition to speeds ...

Augereau, Angelique, Shane Greenstein, and Marc Rysman. "Coordination versus Differentiation in a Standards War: 56K Modems." RAND Journal of Economics 37, no. 4 (Winter 2006): 889–909.