I also researched using the SL30's intercom. I found this thread on the
Van's message board. It basically says the intercom is muted any time there
is radio traffic, which means you can't talk over the radio even if the
incoming transmission isn't for you.  

http://www.vansairforce.com/community/showthread.php?t=1864&highlight=sl30+i
ntercom

This jibes with the troubleshooting section of the installation manual. The
manual says the active frequency has priority over the intercom. Based on
this information, I went with a PM3000 intercom.

-Adam Molny