CLACom works with USB Serial Devices such as Modems and Serial Printers, or any Device where the USB Port on the Device is the equivalent to a Serial Port.
Keep in mind that CLACom only talks to Serial Devices via the Windows Communications API. It knows nothing about the Physical Devices that you attach to a Serial or USB Port.
The USB Device will install a Device Driver that supplements the Windows Communications Driver. A USB Modem Driver, for instance, will add a Phantom Serial Port such as COM 3 or COM 4. You would then use this Serial Port when communicating with the Device.