It's been awhile since I played with the setserial command, so none of that is very fresh in my mind/memory. But something else to keep in mind if you have trouble getting anything to see/recognize the serial port. Check in the bios setup program that the serial port is 'enabled'. Also in the bios, you can generally have the bios 'auto' assign I/O address and IRQ number (probably will default to COM1 in that case), or you can manually select which COM port and I/O address and IRQ number to use. It might be useful just to see what the bios has to say about the onboard COM port.
Here is a link to a post
on the forum describing some of the ways to use the setserial command to both query and set serial port parameters which you might find helpful. If you do a search on the forum using 'setserial' as the search criteria, you'll find many threads to browse through.
Minicom is not an easy beast to use at first try. You will need to run it as root, and then press the CTRL-A and then Z (not all three at once... CTRL and A keys together, release, then press the Z key) to get the menu options. You'll need to use CTRL+A then P to bring up the 'comm Parameters' menu, where you tell minicom which /dev/ttyx to use and other settings such as baud rate to use.
Once that is set up properly, then you should be able to just type something like ATZ in the minicom terminal, and, if all is working as it should, get back some response from the modem, like
If you can get that far, then you know you have a working serial port and a working modem.