INSTALLATION OF OpenSER on Linux ( CentOS )
1. First install the following dependencies that will be needed to compile OpenSER sources:
  - bison
  - flex
  - mysql
  - mysql-devel
  - subversion (if you intend to use subversion to get its sources
  *you can install the said sources via tarballs or rpms or via yum which I did :-)
2. Now get the source OpenSER package ( I get the latest one which is 1.3.x)
  svn co http://openser.svn.sourceforge.net/svnroot/openser/branches/1.3 sip-server
  or via
  wget http://www.openser.org/pub/openser/latest/src/openser-1.3.2-tls_src.tar.gz
3. Unzip and extract the files
  tar xvzf openser-1.3.2-tls_src.tar.gz
4. cd to the source directory
  cd openser-1.3.2-tls
5. Do following for compilation and installation
  make clean
  make all include_modules="mysql"
  make prefix=/usr/local install include_modules="mysql"
6. Now edit first openserctlrc
  vi /usr/local/etc/openser/openserctlrc
  uncomment the line that says
   DBENGINE=MYSQL
7. Now we can create the database for the OpenSER
  /usr/local/sbin/openserdbctl create
  *Note that upon execution of this command it will create 2 users for OpenSER
8. Now we wil edit first the openser.cfg to enable MySQL support.
  vi /usr/local/etc/opernser.cfg
  You will have to uncomment the following lines:
  - loadmodule "/usr/lib/openser/modules/mysql.so"
  - loadmodule "/usr/lib/openser/modules/auth.so"
  - loadmodule "/usr/lib/openser/modules/auth_db.so"
  - modparam("usrloc", "db_mode", 2)
  - modparam("auth", "calculate_ha1", yes)
  - modparam("auth_db", "password_column", "password")
  - if (!www_authorize("sip.org", "subscriber")) {
  - www_challenge("sip.org", "0");
  - break;
  - };
Make sure you change the two sip.org instances in the above config, to your
domain, or realm. In my case, I changed this to 192.168.2.235 which was the
IP address of this box.
Also, be sure to comment out the following line:
modparam("usrloc", "db_mode",   0)
9. Now let us copy the init script so as to start OpenSER as service ( such as starting it at boot). Copy the openser.init which can be found on the base directory of the OpenSER source. In my case I installed the source on root directory
  cp /root/openser-1.3.2-tls/packaging/rpm/openser.init /etc/init.d/openser
  chmod 755 /etc/init.d/openser
  /sbin/chkconfig --add openser
also before you start the openser correct the path of its service execution
vi /etc/init.d/openser
change the following line
oser=/usr/sbin/openser
with this one since we installed the binaries on path /usr/local
oser=/usr/local/sbin/openser
10. Now you can start the openser service
  /sbin/service openser start
11. To test we will create user / SIP account to test our set up. We can do this by using the openserctl tool
  openserctl add test testpasswd test@192.168.2.235
  *Note you might encounter problem once you issued the command above and complaining for the SIP_DOMAiN. To fix that,
  issue the command as follows:
  export SIP_DOMAIN=192.168.2.235
  Now re issue the command for adding new user / SIP account
12. Test it by registering a softphone and filling up the phone's registration info's. You should be able to register already.
  "Now you have a working SIP Server". Actually I am still exploring it too..... I'll give you some more additional infos whatever turns out during my studied on this software. I am more familiar with tweaking Asterisk not this one. But I heard that using Asterisk/OpenSER tandem is great for offering VOIP services.
  Okey that' all for this tutorial hope this help for those who are just about to start with SER/OpenSER. Cheers to all!!!! And God Bless!!!!!  :-)
Here are some more helpful links:
http://www.openser.org/dokuwiki/doku.php/install:openser-from-svn
http://www.openser.org/mos/view/-OpenSER-Installation-Notes/
http://www.oldskoolphreak.com/tfiles/voip/beginners_openser.txt