asterisk users - Jun 2005 - Help with denighing access to certain numbers by CallerID

Hi,

Asterisk 1.0.7
TE405P - Port 1 - ISDN30 telco
       - Port 4 - Primary Rate connection to Phone system

The system has a mixture of 20+ sip phones and the 50 odd extensions on
the phone system connected to Port 4.

What I want to accomplish is to be able to denigh access to certain
outgoing phone calls by the extension/callerid the call originated from.

i.e. Only certain sip and telephone extensions from the phone system can
dial 0011 (international) numbers, and well I already have the porn/pay
per call 1902 calls blocked already.

The difficulty I am having is a problem with being able to block by the
callerid from the phone system calls, I get the callerid from the
incoming extension no problems but blocking certain numbers by it is the
problem.

I can only really see 2 ways to do it, and it's a little above me and I
was hoping someone has done it and I can get a copy of what they did :-
1. Some sort of api or script in the checks the callerid against an
authorised list.
2. setup up the restricted numbers can only be used with a secret code,
when the number is dialed it prompts the users to punch in an access
code to allow the call.

Any suggestions, anyone already done it can throw me an example,
hopefully trying to avoid several pages of allows for the people who can
uses those numbers.

James