[asterisk-users] Good Book on Asterisk

[Norbert Zawodsky]

Hi everybody!

I have some Linux experience but I'm completely new to asterisk.

I bought a small VoIP-PBX which has Linux (Kernel 2.6.13) & Asterisk
(1.2.12) preinstalled and some basic configuration (Wiht a few
extensions). Now I want to implement something more, fox example
voicemail (storing voicemail data in an extern mysql DB) and so on.

And since I don't want to waste your time with stupid questions ....
... can someone of you recommend a really good book on Asterisk? (To buy
or for download)
... or another online source of information which would be helpful for
someone like me?

I searched Amazon with "Asterisk" and got 21 hits......

Thanks
Norbert