Currently you can't restrict access to specific sets of call handlers via the SA. You can set access levels to all handlers (no access, read only, read/write) but it's an all or nothing kind of thing.
The "owner" field on the call handler is intended for just such functionality at some point. We intend to allow access to the call handler greetings over the phone conversation for the 4.0 release this summer sometime. Access to the call handler greetings will be restricted by the owner field (if you are the owner or are a member of the distribution list that's the owner you can access the greetings, if not you can't). Eventually such restrictions will get into the SA as well but not for 4.0.
Currently in 3.x, however, you can't restrict access to specific handlers on a per user basis.
Jeff Lindborg
Unity Technical Lead/Answer Monkey
Cisco Systems
lindborg@cisco.com
http://www.AnswerMonkey.net (new page for Unity support tools and scripts)