I have just spent about 7 hrs total in getting this sorted with trixbox so I thought I'd post my findings here. Also being new to zimbra didn't help!!
Installing the zimlet
Download AND RENAME! remove the version number like so:
original filename: ch_bnc_asterisk_0.65.zip
new filename: ch_bnc_asterisk.zip
Install the zimlet as described everywhere in this thread either vi cli or adminUI.
Extract the config file and edit - this is what you need to change:
This is the name of your zimbra box - NOT your trixbox! (that caught me out for a while!
The IP address of your trixbox
You can use the default trixbox ones here from manager.conf. Defaults are admin and amp111 - but of course you have changed the passwords haven't you?
Not too sure if this affects trixbox, but working ok here
The context taken from the extension settings in FreePBX
I changed this to be blank
My trrixbox simply needs a 9 to dial out so add your prefix here!
Configure the zimlet as described elsewhere, restart mailboxd and then go to your webUI, under zimlets, right click asterisk, select properties, insert your extension number and context 'from-internal' and click ok.
This has worked for me with trixbox 2.6