Hi Diane -
Assuming you have 25% of your voicemail ports configured for dial out - meaning one or more of the following is selected - MWI, Notification, or TRaP:
I would say at most two. One port for the MWI and one for the notification. Typically these ports are the least busy as they are not used for answering calls. If MWI is turned on and then Unity Connection goes to set the Notification, if the port it just used for the MWI is available it will use that. However if the port is in use, it will go to the next available port that is also configured for dial out. In the unlikely event you only had one port enabled for these functions, my guess would be either notification or MWI would queue waiting for the port to become available. You can run the Remote Port Status Monitor on your Unity Connection system to view port usage in real time - http://www.cisco.com/en/US/docs/voice_ip_comm/connection/7x/troubleshooting/guide/7xcuctsg040.html#wp1057024
Hope this helps! Ginger
