A data bypass system diverts data calls to a central office based modem bank and a data network at the subscriber's discretion. The data call diversion is based on a data service prefix in the user's dialing string. The data bypass device translates a subsequent telephone address of a data service supplier into a data network address. The data bypass system is either analog or digital and has a line card with a switch that selectively connects the subscriber line to the voice switch or to a data switch or router through two respective concentrators. The line card includes a data call prefix detector that controls the switch in response to a data call prefix that precedes a data call telephone number. The analog bypass system diverts a data call to a modem and a data network before the data call reaches a voiceband filter and an A/D converter of the line card, while the digital bypass system diverts the data call through a wideband filter and an A/D conversion before applying the data call to a modem accepting a digitized line signal. The digital bypass system utilizes a line card with two filter and A/D converter modules, one for voice calls and another for data calls. Instead of being in each line card, all the line cards share a telephone number and data service prefix detector located following the voice call concentrator.