read this to figue out how to setup the contexts:
http://forum.asterisk2billing.org/viewtopic.php?t=7
it might not be exactly how you want it but at least you should see the contexts how the contexts hang together and relate to each other so that if you want so you could do something else like set your device's context to "a2billing" and understand the consequences
read this to figure out how to supress the request for pin
http://forum.asterisk2billing.org/viewtopic.php?t=479
as to what command you should use to install read this:
http://asterisk2billing.org/html/c200.html
http://asterisk2billing.org/html/c383.html
If you need more help with "installation" file your questions under the "INSTALL" category