Using Exchange Unified Messaging Secondary Dial Plans with Lync and Cisco Communications Manager

Ever been in that interoperability scenario where you have Cisco CUCM and Lync with two different voicemail systems? How do you consolidate down to one voicemail platform? Well Exchange UM secondary dial plans might be your answer.

This is a somewhat of a mystery configuration that has been around since Exchange 2007 SP1 but was originally intended for Faxing or inbound traffic only. The use of OVA from the secondary dial plan was not the intended use even though a subscriber access number needs to be available for inbound routing. Now in Exchange 2010 SP1 this has changed and opened up a new variety of possibilities when integrating legacy IP-PBX’s or PBX’s into Exchange Unified Messaging. My post about this feature focus’s on Lync and CUCM but you could apply most of these same thoughts to number of different scenarios.



The configuration is not to different from what people are used to. You need to create two dial plans, Lync/SIP and CUCM/TelExtn. The biggest configuration difference is really configuring the user to use the secondary dial plan. This can be done through PowerShell or the EMC. Something's to be aware of:

1. Make sure you configure the Lync dial plan for the user first. If the user is already configured for a dial plan other than Lync you will need to disable the user for Exchange UM then re-enable the user with the Lync dial plan. There is not a method to promote a dial plan to primary. The Lync dial plan must be primary otherwise voicemail to Lync will not work.

2. The MWI on the secondary dial plan will not be available. MWI will only be available for Lync as the primary and not the Cisco IP Phone although the MWI for Lync will light no matter if the voicemail is received on Lync or CUCM. The UM  Server  reports only the primary dial plan and extension to the mailbox server when it receives a voicemail. The mailbox assistant works out whether the MWI should be lite based on the primary dial plan information and requests the SIP notify be sent by the UM server (that’s the simple version).

3. One of the interesting pieces to this configuration is that the users extension can be the same for each dial plan. As long as the extension is unique within the dial plan there is little issue with having the same number in both dial plans.

4.Each dial plan requires its own subscriber access number for inbound routing. How a user reaches Outlook Voice Access is really up to you but the secondary dial plan’s SA number will be the number a user accesses when they press the voicemail button on the Cisco IP phone. This is part of the voicemail profile in CUCM which has to be set to SA of the secondary dial plan. With two numbers to access SA it could be confusing for a users if they get prompted for extension and pin rather than just the pin. In the end it’s the same mailbox so you just have to decide what Extension and SA numbers a user has to use for OVA and communicate that effectively.

Below are some useful links:

Understand secondary dial plans in Exchange 2010 SP1:

Understanding MWI SIP Notify in Exchange 2010:

Configuring CUCM with Exchange 2010 UM:

Comments welcomed.



  1. Well thank you so much for this detailed and useful instructions.

  2. Hi, thankyou for the great article.

    I have a customer in a very similar situation (migrating from Legacy to Lync), where they need a period where voicemails will need to be deposited into either mailbox.

    This company is also a big users of Auto Attendants. If we were to migrate their legacy Auto Attendants over to Exchange, how would the Directory Lookup and outbound routing from Exchange work with a secondary dial plan? i.e. if a PSTN user calls the AA, finds the person they are looking for in the Directory and initiates a call to them, would it always use the Primary Dial Plan (the Lync gateway in your configuration above) to route that call to the user?

    1. I am not 100% sure but going by the link below it will depend if you search by name or extension I believe. If you search by name it will give the primary. If you search via extension and use the secondary dial plan extension it should resolve to the user but I am not 100% if the feature will function and call out or only give you the choice to leave a voicemail.

      A search of the directory for a user who hasn't been authenticated will follow these rules:
      The user being searched for will be found and the option to leave a voice message or call the user will be offered only if the user is UM enabled and has a primary extension on the called dial plan. If so, a search by name, alias, and primary extension will find the user. However, a search by secondary extension won't find the user.

      If the user being searched for is UM enabled, has a secondary extension on the called dial plan, and the option Features > Callers can contact > Anyone on the default global address list is selected on the called dial plan, then a search by name, alias, and secondary extension will find them. However, the option to leave voice mail will be offered to the caller, and there will be no option to call them.

      To find and be able to either call or leave a voice message for a user, the caller must call the pilot number of the user's primary dial plan and search by name, alias, or the user's secondary extension. If the user's secondary pilot number is called, they will only be found if the Callers can contact option is set to global address list (GAL). In this case, only the option to leave a voice message will be provided.

  3. How do you configure a user to have a secondary dial plan? I can't see an option for this in the EMC as a user can only be associated with one Mailbox Policy. So how do i apply both Lync and Call Manager dial plans to a user?

  4. Ok firstly i couldn't see any option to do this in the EMC. Its either the EMS or ADSI.
    Secondly the information in the Exchange help file is incorrect. It says it only works with Ex2010 SP2/SP3 but the capability is present in SP1.
    Thirdly the command that you need to run is a bit opaque and not well documented. It should be: Set-Mailbox "User1" -SecondaryDialPlan "4digitdialplan" -SecondaryAddress 1111. This adds the additional dial plan to the UMenabledUser, as well as the extension number.
    The Secondary Dial Plan and Secondary Address are appended to the ProxyAddress attribute in AD and thus visible in the shell under ProxyAddress which was a tad confusing as i expected to see attributes for -SecondaryAddress and -SecondaryDialPlan as part of the mailbox schema.


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