Depending on which version of asterisk you are running and/or which linux version you have, the following should work:
First download the asterisk source code and place them in /usr/src
Then check for dependencies as follows:
yum -C list ncurses ncurses-devel openssl zlib zlib-devel curl
tar -zxvf libpri-1.4.x.tar.gz
tar -zxvf dahdi-linux-complete-2.0.tar.gz
tar -zxvf asterisk-1.6.x.tar.gz
;PBX Modules ---- deselect pbx_ael Extras Sound Packages --- select EXTRA SOUNDS EN GSM
;F12 to save and exit
lsmod | grep dahdi
:If all went well, you should now have asterisk up and running on your box. The make sample commands above, made sample sip.conf and extensions.conf files. These files are very verbose. You may want to rename them and recreate new files. The following sample should get you going.
;Configure users, peers friends
; save and the sip reload
exten => xxx,1,Dial(SIP/sipuser)
:This is a very quick and simple sample. Suggest that you invest in one of the many good publications that are available. Most can be found on the web for nothing.