Checking if modem line busy

Noobie here, so this may be a really dumb and simple question, but I can't seem to resolve it so far.

I want to simply test if the phone line is in use before I have my program dial the modem (VB6). I'm trying using MSComm but even the .portopen command returns an error. Shouldn't I be able to set portopen = true then output AT commands to test for use? Is there an easier way to silently be sure no one is talking on the phone line before the modem dials?

I'm probably missing the obvious, please go easy on me :).

Thanks

You can't open a port that doesn't exist - that's how you test for existing ports, by opening them and trapping the error. It sounds as if the port you think you have isn't really the port you have. Run through ports 1 to 30, trying to open them and having the program tell you which ones opened. (I assume that the computer has either at least one real RS232 port, or you have at least one USB->serial adapter plugged in and working properly.)