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Yes, that is right. You need to have DAG so a mailbox database can be activated on more than one node and voice mail can be delivered if one node fails.<br />
Also keep in mind that you need to have some kind of failover scenario for the servers receiving the calls - &nbsp;for example you can use Windows NLB to route callls to several UM servers - not sure about your setup whether the UM role is also combined with something else.
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Yes, that is right. You need to have DAG so a mailbox database can be activated on more than one node and voice mail can be delivered if one node fails.
Also keep in mind that you need to have some kind of failover scenario for the servers receiving the calls -  for example you can use Windows NLB to route callls to several UM servers - not sure about your setup whether the UM role is also combined with something else.

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we are using a hardware load balancer. &nbsp;So the dial plans and auto attendant live on all servers? &nbsp;that would make sense to me.
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we are using a hardware load balancer.  So the dial plans and auto attendant live on all servers?  that would make sense to me.

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In my scenario i have 3 multi-roled exchange 2013 servers<br />
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The dial plan and auto attendant lives all &nbsp;3 exchange servers?<br />
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you would need to implement a DAG because if server 1 is down, then voice mail won't be delivered to the mailboxes in database 1 and that is on server 1?
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In my scenario i have 3 multi-roled exchange 2013 servers

The dial plan and auto attendant lives all  3 exchange servers?

you would need to implement a DAG because if server 1 is down, then voice mail won't be delivered to the mailboxes in database 1 and that is on server 1?

unified messaging exchange 2013 / lync 2013

Exchange is the server side of a collaborative application product that is part of the Microsoft Server infrastructure. Exchange's major features include email, calendaring, contacts and tasks, support for mobile and web-based access to information, and support for data storage.