November 8th can be called the relaunch of development for the Asterisk/Drupal module. I worked with the Asterisk PBX as an application a few years ago. At the time I found these resources extremely helpful:
http://trixbox.org/
TrixBox is a GPL application that rolls Asterisk, a full Linux install, Apache, MySQL and PHP and a variety of Asterisk supporting applications such as Festival into a single ISO.
If you haven't touched Asterisk before and want a head start, put this onto an extra PC and you will be golden!
Sipura 2002s and 3000 ATA (Analog Telephone Adapter). This is a fairly older piece of hardware but still very useful. The 2002 has 2 Analog phone jax (FXO) and a network jack as well as a DC power supply, and the 3000 has a single FXO port and another FXS (plugs into the street's legacy phone system from Fairpoint in my case) and the same Network and power supply as the 2002 device.
Either of these will allow you to interface your standard phone and hand set into your Asterisk PBX. I typically like the Sipura 3000 since it can be configured to allow you to have you standard telephone plugged into the the FXO jack and the Fairpoint steet service to be plugged into the FXS port, while still interfacing with the IP network. This allows you to recieve calls to your handset from anyone calling from a standard line to an internet line, even from a skype caller. (Skype recently released an Asterisk module I believe ... http://blogs.digium.com/2009/02/23/skype-for-asterisk-update/)
http://nerdvittles.com/
Ward Mundy, an enthusiastic Lawyer/Linux nerd, has been blogging on Asterisk forever. He has an excellent collection of resources for the platform
http://axvoice.com/
My current Internet phone carrier. Interfaces well with both Asterisk or the Sipura devices mentioned above.
http://broadvoice.com/
I've used them in the past. Fairly good service, had issues with latency on calls for a while and switched to Axvoice.