Hello,
Not sure if you are a Voicemail Only install or Unified Messaging Install.
If a Voicemail Only install then you could use either DIRT (Disaster Recovery Tool) or Cobras http://ciscounitytools.com/Applications/General/COBRAS/COBRAS.html. (This is link to Video and help file)
Corbras has become a more popular choice since it release. Major benifits include it can be restored to newer versions of Unity as opposed to attempting an upgrade. Also you can restore partial or full backup to a currently populated database.
You can check out the following help file to get more detail. http://ciscounitytools.com/Applications/General/COBRAS/Help/COBRAS_Briefcase/COBRAS_Briefcase.htm
Also both these tools can backup Exchange.
Generally if you are using a Unified Messaging you are already backup up your Exchange with some type of software such a Backup Exec for example. Therefore you could still use Cobras or DIRT to backup Unity.
Hope that helps.
Thanks,
Scott
