Freeswitch depends on several out of tree libraries.  All of freeswitch depends on APR, and mod_exosip depends on osip, exosip, jtrhead, and jrtplib.  
Download locations and links for details can be found below.

Apr info available at: http://apr.apache.org

Download Locations:
apr: http://apache.mirrors.versehost.com/apr/apr-1.2.2.tar.gz

Backup Download Locations:
apr: http://www.sofaswitch.org/mikej/apr-1.2.2.tar.gz


Exosip\Osip info available at: http://www.antisip.com/

Download Locations:
osip: http://www.antisip.com/download/libosip2-2.2.1.tar.gz
exosip: http://www.antisip.com/download/libeXosip-0.9.0.tar.gz

Backup Download Locations:
osip: http://www.sofaswitch.org/mikej/libosip2-2.2.1.tar.gz
exosip: http://www.sofaswitch.org/mikej/libeXosip-0.9.0.tar.gz


Jthread\Jrtplib info available at: http://research.edm.luc.ac.be/jori/page.html

Download Locations:
jthread: http://research.edm.luc.ac.be/jori/jthread/jthread-1.1.2.tar.gz
jrtplib: http://research.edm.luc.ac.be/jori/jrtplib/jrtplib-3.3.0.tar.gz

Backup Download Locations:
jthread: http://www.sofaswitch.org/mikej/jthread-1.1.2.tar.gz
jrtplib: http://www.sofaswitch.org/mikej/jrtplib-3.3.0.tar.gz