You have three methods:

1 - COR list. Permanently block certain calls from certain phones and cannot be overridden.

2 - PIN login & after-hours. Once logged with a per-phone pin in you can dial certain patters and also define a time schedule for this to happen.

3 - Custom steering digits. You create special prefixes to allow certain calls and this code is given to people, kind of like an account number.

1 & 2 are explained in the sysadm guide and others CCO documents. 3 - is not but easy to figure out.

Hope this helps, please rate post if it does!