asterisk users - Aug 2008 - Explain t38 and how it relates to Asterisk

Hi guys,
What's the easiest way to explain to someone the state of t38 with Asterisk
and what does / doesn't work in 1.4 stable from an end user point of view?
I have a friend who uses an ata to connect to an Asterisk server and he asks
me why he can not send faxes even though both end points support t38 and I
have the canreinvite option set to yes in sip.conf
I also have t38pt_udptl = yes

Tom