1. currently there's no automatic deletion of messages built into Unity. There are MS tools for doing this kind of thing (Mailbox Manager) that are built into Exchange 2000 and come with Exchange 55 SP2 or later. It's a little hairy to use but can do what you want. For the record, the Customer Applications Team here is currently working on a specification for a "mailbox manager tool" that can help voice mail only type sytems setup such rules easily for doing just this type of thing.
2. You can adjust message length on a per subscriber basis if you want... even lowly, hard working mail clerks can have longer messages sizes if they want. This is set on the messages page in the SA and can also be changed for groups of users at one time using the Bulk Edit utility.
3. The Mailbox limits are set in Exchange... this can be done on a per user basis if you like and yes, you can make a mailbox unlimited if you want.
Jeff Lindborg
Unity Technical Lead/Answer Monkey
Cisco Systems
lindborg@cisco.com
http://www.AnswerMonkey.net (new page for Unity support tools and scripts)