How to make Linux Box  a dial-up server
Settings imply to ttyS0 alias cua0 alias COM1
Using uugetty and setserial
4. Steps - if you have your modem configured correctly

1. /etc/rc.d/rc.serial script (Serial line init during boot)
2. /etc/inittab config according to used serial line
3. /etc/gettydefs config operational speed
4. /etc/conf.uugetty.ttyS0

Examples
rc.serial
#vytvorene 24.6.1998 v snahe spravit z jakubpc dial-up server
#set up the port to go to 115,200 baus when 38400 requested
#assumes that your modem can run at 115,200 baud.
/bin/setserial /dev/modem spd_vhi

inittab
#
# inittab       This file describes how the INIT process should set up
#               the system in a certain run-level.
#
# Author:       Miquel van Smoorenburg, 
#               Modified for RHS Linux by Marc Ewing and Donnie Barnes
#

# Default runlevel. The runlevels used by RHS are:
#   0 - halt (Do NOT set initdefault to this)
#   1 - Single user mode
#   2 - Multiuser, without NFS (The same as 3, if you do not have networking)
#   3 - Full multiuser mode
#   4 - unused
#   5 - X11
#   6 - reboot (Do NOT set initdefault to this)
# 
id:3:initdefault:

# System initialization.
si::sysinit:/etc/rc.d/rc.sysinit

l0:0:wait:/etc/rc.d/rc 0
l1:1:wait:/etc/rc.d/rc 1
l2:2:wait:/etc/rc.d/rc 2
l3:3:wait:/etc/rc.d/rc 3
l4:4:wait:/etc/rc.d/rc 4
l5:5:wait:/etc/rc.d/rc 5
l6:6:wait:/etc/rc.d/rc 6

# Things to run in every runlevel.
ud::once:/sbin/update

# Trap CTRL-ALT-DELETE
ca::ctrlaltdel:/sbin/shutdown -t3 -r now

# When our UPS tells us power has failed, assume we have a few minutes
# of power left.  Schedule a shutdown for 2 minutes from now.
# This does, of course, assume you have powerd installed and your
# UPS connected and working correctly.  
pf::powerfail:/sbin/shutdown -f -h +2 "Power Failure; System Shutting Down"

# If power was restored before the shutdown kicked in, cancel it.
pr:12345:powerokwait:/sbin/shutdown -c "Power Restored; Shutdown Cancelled"


# Run gettys in standard runlevels
1:12345:respawn:/sbin/mingetty tty1
2:2345:respawn:/sbin/mingetty tty2
3:2345:respawn:/sbin/mingetty tty3
4:2345:respawn:/sbin/mingetty tty4
5:2345:respawn:/sbin/mingetty tty5
6:2345:respawn:/sbin/mingetty tty6

# Run xdm in runlevel 5
x:5:respawn:/usr/bin/X11/xdm -nodaemon

# Dial in lines enabled in standard runlevels
S0:2345:respawn:/sbin/uugetty ttyS0 F38400 vt100

gettydefs
# [ put this file in /etc/gettydefs ]
#
# This file contains the startup and final flags for the
# tty lines.  Each line starts with a SPEED value; this is
# the same SPEED that you pass to [uu]getty.  Note that the
# SPEED identifier is just a string; use whatever names
# you want.
#
# The blank lines in this file are important (so I hear).
#
# The flags are the same flags you would pass to the stty
# program.
#
# Format: #  #  ##
#
#
# Virtual Console entry
VC# B9600 SANE CLOCAL # B9600 SANE -ISTRIP CLOCAL #@S login: #VC

# 38400 fixed baud Dumb Terminal entry
DT38400# B38400 CS8 CLOCAL CRTSCTS # B38400 SANE -ISTRIP CLOCAL CRTSCTS #@S login: #DT38400

# 19200 fixed baud Dumb Terminal entry
DT19200# B19200 CS8 CLOCAL # B19200 SANE -ISTRIP CLOCAL #@S login: #DT19200

# 9600 baud Dumb Terminal entry
DT9600# B9600 CS8 CLOCAL # B9600 SANE -ISTRIP CLOCAL #@S login: #DT9600

# 230400 fixed-baud modem entry
F230400# B230400 CS8 CRTSCTS # B230400 SANE -ISTRIP HUPCL CRTSCTS #@S login: #F230400

# 115200 fixed-baud modem entry
F115200# B115200 CS8 CRTSCTS # B115200 SANE -ISTRIP HUPCL CRTSCTS #@S login: #F115200

# 57600 fixed-baud modem entry
F57600# B57600 CS8 CRTSCTS # B57600 SANE -ISTRIP HUPCL CRTSCTS #@S login: #F57600

# 38400 fixed-baud modem entry
F38400# B38400 CS8 CRTSCTS # B38400 SANE -ISTRIP HUPCL CRTSCTS #@S login: #F38400

# 19200 fixed-baud modem entry
F19200# B19200 CS8 CRTSCTS # B19200 SANE -ISTRIP HUPCL CRTSCTS #@S login: #F19200

# 9600 fixed-baud modem entry
F9600# B9600 CS8 CRTSCTS # B9600 SANE -ISTRIP HUPCL CRTSCTS #@S login: #F9600

# 2400 fixed-baud modem entry
F2400# B2400 CS8 CRTSCTS # B2400 SANE -ISTRIP HUPCL CRTSCTS #@S login:  #F2400

# 230400 autobauding Modem entry with hard flow control
230400# B230400 CS8 CRTSCTS # B230400 SANE -ISTRIP HUPCL CRTSCTS #@S login: #115200

115200# B115200 CS8 CRTSCTS # B115200 SANE -ISTRIP HUPCL CRTSCTS #@S login: #57600

57600# B57600 CS8 CRTSCTS # B57600 SANE -ISTRIP HUPCL CRTSCTS #@S login: #38400

38400# B38400 CS8 CRTSCTS # B38400 SANE -ISTRIP HUPCL CRTSCTS #@S login: #19200

19200# B19200 CS8 CRTSCTS # B19200 SANE -ISTRIP HUPCL CRTSCTS #@S login: #9600

9600# B9600 CS8 CRTSCTS # B9600 SANE -ISTRIP HUPCL CRTSCTS #@S login: #2400

2400# B2400 CS8 CRTSCTS # B2400 SANE -ISTRIP HUPCL CRTSCTS #@S login: #230400

Last but definitively not least conf.uugetty.ttyS0
#/etc/conf.uugetty.ttyS0
#for more details man uugetty
SYSTEM=jakubpc
VERSION='/bin/uname -s -r'
LOGIN=/bin/login
ISSUE=/etc/issue
INITLINE=cua0
TIMEOUT=60
HANGUP=YES
INIT="" \d+++\dAT\r OK\r\n ATH0\r OK\r\n AT\sZ4\r OK\r\n \d+++\dAT\sE1\sQ0\sV1\sX4\r OK\r\n
# par slov k init retazci ATH0 hangup ATZ4 reset to AT&F1 USR Sportster RTS/CTS
#template, then wait \d+++\d ATE1 local echo on, ATQ0 messages on, ATV1 verbal 
#messages (codes), ATX4 displayed codes see modem manual
# waitfor string... if this sequence of characters is received over the line,
# a call is detected.
WAITFOR=RING
# this line is the connect chat sequence.  This chat sequence is performed
# after the WAITFOR string is found.  The \A character automatically sets
# the baudrate to the characters that are found, so if you get the message
# CONNECT 2400, the baud rate is set to 2400 baud.
#
# :   ... (chat sequence)
CONNECT="" ATA\r CONNECT\s\A
DELAY=2
#DEBUG=010              # uncomment this for debug output
#
# END /etc/conf.uugetty.ttyS0