RAS for Windows NT 4.0 supports Unimodem modems. If your communications device is not supported by Unimodem, it may be supported by Modem.inf (%systemroot%\System32\RAS\). To configure RAS to use Modem.inf, edit:

HKEY_LOCAL_MACHINE\Software\Microsoft\RAS\Protocols

Add Value name EnableUnimodem as type REG_DWORD and set it to 0.

In Control Panel / Networks / Services / Remote Access Service, click Properties. Remove all ports that are defined in the RAS Setup dialog. Now, click Add and add them back.

RAS will now use Modem.inf.