Just finished the first successful test of the Asterisk install. I'm actually using a VoIP account over on our client's network as an inbound communications channel and connecting via a PSTN (regular telephone network) phone to the box sitting next to me. The Asterisk box is behind a NAT-ing firewall configured to trigger an opening for the RTP packets when SIP packets go through.
Apparently the Asterisk the Future of Telephony book is a little ahead of the Gentoo AMD64 stable version of Asterisk, as my version doesn't support the 'n' numbering for "priorities". Once I figured that out the test worked perfectly.
Which is something I have to mention; there's an enormous amount of the book occupied with the compilation, installation and setup of Asterisk. On Gentoo it was so simple that I didn't even know which version I had installed (hence didn't know that I wasn't using the 1.2 version), I just told it to emerge (without paying attention to the particular version it was going to install) and it downloaded and installed everything, even giving me helpful hints as to where to go for documentation, how to enable access to sound cards and the like. Gentoo can be extremely cool that way, but it does tend to encourage a certain laziness where if it isn't in portage you just don't bother with it.
Anyway, back to playing now.