A previous poster mentioned the same thing, with no response:
http://lists.digium.com/pipermail/asterisk-users/2004-
December/080161.html
Fresh asterisk 1.0.5 install on FC3, started with make samples,
nothing fancy. It's so bland, I'm surprised the list isn't full of
people having the same
Thanks to Pau (the original person to pose the question on this list), it's fixed. The firewall was getting in the way. I needed to open up UDP ports 1 to 2 for RTP traffic.
See the following for more info:
http://www.voip-info.org/tiki-index.php?page=Asterisk%20config%20rtp.conf