====== MWI Subscription ======

  * This method is for if a phone doesn't support anonymous SIP notify, but supports subscription. 
    * The DuVoice system can handle SIP subscriptions for a **maximum of 250 extensions**. 
    * This limit is due to the SIP stack and not a configuration setting which can be changed.

===== Requirements =====
  * DuVoice v7.1 (and above).
  * Phone support custom 3rd party address for Message Waiting subscription. 
  * Phone extension must match mailbox number or have the ability to specify the account.
  * DuVoice must be able to send network packets directly to the gateway.
  * DuVoice must be licensed for SIP.

===== Mailbox =====

  * No special configuration must be performed in the mailbox.
  * Leave the MWI addresses as the extension which is the default setting. Using a SIP address will cause subscriptions to fail.