Addendum:

Why not a course on Twilio?

@John Britton:

Neat; is this sortof an 'open'-skype? I guess that your company eliminates the need to purchase SIP lines and all that good stuff?

If you're interested in this couse I suggest you check out http://twilio.com as an alternative to using Asterisk.

disclosure: I work at Twilio

Will you discuss how to implement custom logic within Asterisk? e.g., if number-pressed = 123, then do... xyz? Or extending asterisk with other things, for example, text-to-speech engines or speech recognition? (More generally, allowing asterisk to interact with scripts/programs outside of it?)