I'm assuming these emails originate from the same sender.
If so you could easily grab these early in the workflow. Here is what I would do logically in the workflow:
1. If from voicemail
2. Then repleace empty subject with "Voicemail ticket"
3. and Replace empty body with "Voicemail ticket created from email"
After this is done you can continue process the message in the workflow normally, either by creating a IM-ticket directly or a EM-ticket. Just like André mentions above you need to watch the size of the attachment. I would guess the sound files is not anywhere near the size limit.