OK, Neil I'll give it a try.
> On my system, I made sure that USBCOM.SYS was the first device= statement. That ensures that the USB com port comes before all the other com ports.
I'll Un-REM <USBCOM.SYS> and move it up to the top of the Device lines. I'll also REM the <USB.COM> line. And, of course, I'll reconnect the USB cable to the modem.
> IBM File and Print services also shares COM ports, so if you install that, it will grab a com port.
Here I'll have to dredge up my recollection of how IBM File and Print services differs from CUPS. I have an HP DeskJet 3052a connected via a USB cable. Opening the Properties for it shows that it utilizes a CUPS Port and, of course, is identified by a network IP Address. The Output Port window also shows COM ports 1 through 4, and as they are not "shadowed" they don't seem to be utilized by any printer.
And RM View doesn't show that either IRQ 4 or 3 are utilized by any device. Maybe then there ought not be any conflict?
> I didn't bother installing COM.SYS, apparently.
As said, I'll REM out <COM.SYS> and see how this goes.