Leave a Msg use case - simple scenario walkthrough

1. User types an extension:
   • Telephone sends number to Connection
   • Connection collaborator of Telephone
   • Place the 2 cards adjacent)
2. Connection asks MailSystem to find appropriate MailBox object
   • Vaguely included in the "manage mailboxes" responsibility
   • Keep MailSystem and Mailbox cards close to Connection card
3. Connection asks Mailbox for its greeting
   • Add "manage greeting" to Mailbox responsibilities
   • add Mailbox as a collaborator of Connection