| Class | Description | 
|---|---|
| Connection | 
 Connects a phone to the mail system. 
 | 
| Mailbox | 
 A mailbox contains messages that can be listed, kept or discarded. 
 | 
| MailSystem | 
 A system of voice mail boxes. 
 | 
| MailSystemTester | 
 This program tests the mail system. 
 | 
| Message | 
 A message left by the caller. 
 | 
| MessageQueue | 
 A first-in, first-out collection of messages. 
 | 
| Telephone | 
 A telephone that takes simulated keystrokes and voice input
   from the user and simulates spoken text. 
 |