Since each modem has an associated serial port and the port has both hardware and software, there are three parts to configuring a modem:
The above omits a few other things that "setserial" can do besides locating the serial ports. But normally you don't need to use them. Setserial may be used in the future to enable super-high speed.
Communication programs include
wvdial (for PPP) and
mgetty for dial-in. Such communication programs require that you configure them, although the default configuration they come with may only need a little tweaking.
Unfortunately the communication program doesn't locate the serial port. This "locating" is the low-level PnP configuring of the serial port: setting its IO address and IRQ in both the hardware and the driver. If you are lucky, this will happen automatically when you boot Linux. Setting these in the hardware was formerly done by jumpers and then running "setserial" but today it's done by "Plug-and-Play" software. You may still need "setserial". So if Linux (or the wvdial program, etc.) doesn't report what serial port your modem is on, then you can try to find it yourself per the next section but it may not be easy.