This graph shows the time to transfer various amounts of information. If I'm transferring a floppy, it only takes 8 minutes on POTS. On the other hand, if I wanted to transmit 20 floppies, the size of Word 6.0, POTS doesn't do it. ISDN still takes 30 minutes.
And so what's a reasonable bandwidth if we're going to transfer anywhere from a 1995 CD with 600 megabytes to the next standard 9 Gigabytes CD due in the next few years. You really need 10 megabits or more. So I say 25 megabits because that's an ATM standard and that's a reasonable engineering target. Cambridge England has this in prototype form. It doesn't hurt our phone bills since telecos are spending our money on inferior alternatives.