There is one Cisco CallManager Express in each branch site and one in the central site. However, all the IP phones in all locations use a common Cisco Unity server installed in the central site.
Message-Waiting Indication (MWI) on IP phones work properly for all IP phones in the central site. However, it does not work for IP phones at the branch site.
This situation could arise if the branch Cisco CallManager Express is not configured for voice mail access.
For more information, refer to the procedure in the Programming Multiple Cisco CallManager Express Routers to Integrate with a Single Cisco Unity Server section of Cisco CallManager Express 3.0 Integration Guide for Cisco Unity 4.0.
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