Dial-up is a dying business, with AOL, EarthLink, and other providers that used to have primarily modem-based users seeing millions of customers shed each quarter as they switch to broadband. At the time I write this, broadband use among American households is nearing 50 percent, dial-up use about 25 percent, and no access at about 25 percent. Dial-up as a percentage of all Internet access at home was 80 percent five years ago; it's now one-third.
As more Americans switch to cell phones at home; as faster cell networks are deployed; as Wi-Fi service is rolled out as a "dial-up replacement" across entire cities and countries; it seems likely that modems that use analog, public switched telephone network phone lines to place data calls will become an increasingly marginal business.
By 2010, the five percent of households that use dial-up service as Internet access will represent the small proportion of the population for which no other means is possible due to their particular circumstances, such as living rurally, living in an underserved urban or suburban area, or simple cussed preference.
Cost will not be an issue. In fact, I expect that dial-up service might become be available at a premium due to its occupation of a circuit-switched phone line and physical equipment that must be present at the far end of the connection.
Challenge Glenn I Fleishman to a bet on this prediction!