>You can use this control to poll a number of COM ports to find out which, if any, have a modem attached (and switched on).

If you take the polling approach, make sure that it is optional. I had problems with 1 particular app. that automatically polled for modems on start up - with no option to turn it off - unfortunately, I had a serial device attached using a very unforgiving protocol, which required turning off & on again after the app. to allow the main control app. to function correctly. I've also got clients using serial printers, they get annoyed by ATZ at the top of pages.