This icon is pretty common:
I wonder how many people know it comes from something like this:
This great article, The Floppy Disk means Save, and 14 other old people Icons that don’t make sense anymore by Scott Hanselman, has 13 more examples of this. Fun to read.
Smart People I Know 
Reblogged this on missyely and commented:
Interesting post.
I think the voice mail comes from the cassette tape rather than the big bulky ones. The icons to represent actions or devices are usually based on more household items.