“The result is that you will never be able to connect at a speed faster than 53.3 kbit/s.”
The phone network samples voice 8,000 times a second at 7 usable bits, and 7 times 8,000 is 56 kbit/s. Then the FCC caps the power on the line and the real ceiling drops to 53.3. Every 56k modem sold in the U.S. advertised a speed the law forbade it to reach.