Does anyone here uses any other voice products?

I am comfortable with working with callmanager 4.X and CCME. But I want to learn other voice products. I was doing some research and came across Asterisk which is open source. Does anyone here have experience with Asterisks? And can they help someone like me who has no experience with it whats so ever get it up and running? Thanks.
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Comments
An Asterisk expert I knew always had a copy of Asterisk the Future of Telephony with him. I haven't had a chance to read it myself yet, but have heard good reviews from people who have.
I've had the misfortune to use some early versions of a Nortel BCM VoIP PABX aka an Intel PC in an custom box with some special cards. It ran a totally stable and bug free version of NT4... Thankfully they came to their senses and in a later version of the software, they changed it to a Linux based system which has been much more reliable.
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