Found a way to bulk create a .wav file. There are 2 ways of doing this: a) on the front end using Unity Templates and on the back-end using the "Bulk Edit" feature for voicemails, under the "users" section.
I opted for option a). Basically, you have to install the embedded Java recording utility in the voicemail template, under Edit > Greetings. Fair warning - getting Java to work is a pain in the butt....
a) Install Java 7, SU 21 (works the best). It can be found here:
b) In Control Panel > Java in Windows. Enable Java 7, then in the security tab create security exceptions for your Unity connection URL
c) Using IE 11 (not Edge, Chrome or Firefox), put your Unity URL in under the "Trusted Sites" location and restart IE 11.
d) Create a Unity Voicemail Template, with all the settings you want the voice-mail to have
e) In the template, go to Edit > Greetings.
> Under "Callers Hear", click the "Personal Greeting" radio button.
> At the bottom is a small Play/Record button. This is the embedded Java utility. Press the button and accept all of the security warnings.
f) Record your message and save. IE might kick you out when you click save, so go back in and try again.
Now when you use the BAT tool to import your mailboxes, in the "Override CSV Fields", select "Yes" and the voice-mail template you created in d).
