Pretty sure the PC in that picture is a third-party voice mail server, many are standard PCs and use mostly standard PC components, some are proprietary. The one in the picture looks pretty familiar to me but I am having a problem recognizing it, but it might be a Comdial/Keyvoice Small Office Lite or similar Keyvoice PC based server, and if memory servers me right it is about half and half off-the-shelf components and proprietary components, but it has been so long it is tough to remember the details.
The tough part with these isn't usually the hardware, as long as it's standard PC components, the tough part is usually the software... Many used proprietary OSs, and sometimes DOS, OS/2, Coherent, and other various ones, but rarely something the average person has laying around, plus the VM software itself is usually impossible to find as many of those companies are out of business or older models are no longer supported in any way.