If it has no jumpers then it's likely a Plug-and-Play modem which the BIOS may configure when you power one your PC. Typing "pnpdump --dumpregs" should find it. If you need to set or change them use "isapnp". Use the "pnpdump" program to see what changes are possible.
Both PCI and ISA: Use setserial to tell the serial driver
You must find the file where "setserial" is run at boot-time and add a line something like: "setserial /dev/ttyS2 irq 5 port 0x0b8". For setserial v2.15 and later the results of running "setserial" on the command line may (or may not) be saved to file named serial.conf or autoserial.conf. It might be in say the /etc directory or in the /var/lib/setserial directory (use "locate to find it). it runs each time you boot. See What is Setserial for more info. See the next subsection All Modems for further instructions on quick installation.
Use MS Windows to set the BIOS (A last resort method)
If you are using the BIOS to configure you may attempt to use MS Windows9x to "force" the BIOS to set a certain IRQ and/or IO. It can set them into the PnP BIOS's flash memory where they will be used to configure for Linux as well as Windows. See "Plug-and-Play-HOWTO and search for "forced" (occurs in several places). For Windows3.x you can do the same thing using the ICU under Windows 3.x. A few modems have a way to disable PnP in the modem hardware using software (under Windows) that came with the modem.
All Modems
Plug the modem into a telephone line. Then configure a dialing program. If you have an Internet Service Provider (ISP) you might configure one of these : wvdial, pppconfig, gnome-ppp, modem lights (Gnome) or kppp. They not only dial out but start PPP, which you need to connect to the Internet. Otherwise, you might try configuring the minicom dialer which isn't designed for connecting to the Internet, but is good for testing. Whether it's minicom or a dialer that starts PPP, set the serial port speed to a baud rate a few times higher than the bit rate of your modem. See Speed Table for more details on the "best" speeds to use. Tell it the full name of your serial port such as /dev/ttyS1 (or /dev/ttys/1).
Minicom is one way to set up and test your modem. Set hardware flow control (RTS/CTS). With minicom you may check to see if your modem is there (and ready to dial). Once you've set up minicom, type the command: AT, hit enter and you should see an "OK" response which comes directly from the modem. See Dialing Out with Minicom.
