I wonder if this is a feature or not. Singapore does not have Google Voice yet. Anyway, it seems that Google has indexed some of the voice messages. Of course, there are test messages. However, some of them are too vulgar to be test message 
. Anyway, enjoy these messages.
Here is how you can listen to them.
Key in: -
site:https://www.google.com/voice/fm/*
in Google Search and you will know how to do the rest. “Enjoy”
(source)
