Some ISPs may diversify and sell voice calls. Ascend Communications agreed to purchase Cascade Communications, a fitting combination of networking technologies. All optical networks are on the horizon. Check out Ciena's MultiWave 1600, allowing a monomode fiber bandwidth increase from 2.488 Gbps to 39.81 Gbps. Old TDM cuts off at about 2.488 due to the limited silicon switching speed.
Electrons are heavy and slow compared to photons.
Optional fiber downlink modules are available as well. Cisco purchased Telesend, an ISDL equipment manufacturer. Hayes Microcompter started shipping many different 56k modems. They are based on Rockwell's and Lucent's K56Flex technology. Motorola's Rockwell based 56k modems are delayed due to throughput problems under some circumstances.