The universal modem driver (Unimodem) component provides the infrastructure necessary for applications to communicate with a modem. Communication with the modem can take place using the Telephony API (TAPI), which is used by such applications as the Remote Access Service (RAS), HyperTerminal, Phone Dialer, or through a direct interface with the communication port.
To configure this component, you must first select the underlying transport substrate for the communications device, for example, a serial, a USB, or a modem driver without a controller.
On first boot, your device will be detected and you must then install a modem. After installation, applications will have direct access to the modem.
For more information about the Unimodem component, see the Modem Developers Kit (MDK) at this Microsoft Web site