VoIP Hacks book

 VoIP Hacks by Ted Wallingford from O'Reilly article

Some free PDF chapters including:

Hack 3: Wire Your House Phones for VoIP
Hack 11: Sound Like Darth Vader While You VoIP
Hack 40: Skype with Your Home Phone
Hack 55: Link Two Asterisk Servers with PSTN
Hack 96: Build a Standalone Voicemail Server in Less Than a Half-Hour