http://www.voip-info.org/wiki/view/T.38

http://ictfax.org/content/ictfax-installation-guide-centos-fedora

http://sourceforge.net/projects/t38modem/files/t38modem/2.0.0/  T.38 Fax modem

http://www.fabulatech.com/virtual-modem-download.html virtual modem