If you check the topic, you'll see we're talking specifically about modems, please tell me about all the modem specific drivers you see in CONFIG.SYS or AUTOEXEC.BAT? ::) Could also be tablet and soundcard drivers.
There are memory and CDROM and mouse drivers in CONFIG.SYS in most DOS machines. The terminal program is responsible for establishing a rudimentary interface for downloading and uploading files and for accessing the client PC from the server if they aren't peers. Thus, a machine with a USR Courier V.Everything ISA modem would access it through the USR V90/V92 init string in Telix, not by any direct-to-DOS driver. But you may need to use MODE in AUTOEXEC.BAT to set up the RS232 port characteristics for the modem's COM port. Modems are usually handled by the terminal program (ProComm, Offline Express, Telix, Omen) used in DOS, not by a CONFIG.SYS driver.