For speeding it up, there is no option I am aware of. It is what it is for migrating into the database. It also depends on the hardware you are using for Connection. If its a 7925 or less, its going to be slow.
Your other option is to migrate in phases in a few night windows. You will need to do some CUCM modifications for VM profiles. If I have a large group to be migrated, I typically do the following:
- either migrate in phases (200-500 a night) then do support the following day, repeat each night until completed.
- Or setup all new voicemail boxes, then let the users know we will be populating their old voicemail over the next 24-48 hours.
Your other option, which does not sound possible, is to start them with new mailboxes. Leave the old server up and running for a few months for them to clean out their old voicemails. Say it is a legal issue for retaining messages, etc.