Maybe this can help http://www.math.sunysb.edu/~comech/tools/PCImodems.html (or this http://linmodems.technion.ac.il/ )

This is from another forum:

"Alternatively, try ls -l /dev/modem to find out the com port. You can also do things like ls -l /dev/ttyS2, etc. All from Command line. The latter gives the c 4 68 part of it. Also see man pages on ls. Watch the spaces in the code.

Two other handy pieces of code, from cmnd line as su:

mknod /devttyS2 c 4 68 Here S2 is COM3, etc.
(this sets S2)

ln -s /dev/ttyS2 /dev/modem Links e.g. S2 to /dev/modem"