At last I figured how to split the haves/havenots!
THIS link reveals 6 countries:
Spain, Germany, Singapore, Italy, France, Hong Kong.
If you try es.voice.yahoo.com yourself, you'll be redirected to YOUR "local" version, but thanks to Google's "caching" you can see the ORIGINALS here - all showing Yahoo PC-to-Phone AVAILABLE NOW, IN those countries!
From local knowledge, I happen to know that au.voice.yahoo.com applies the same (dunno why Google never spotted it!), and it covers New
Zealand as well as
Australia, so that's EIGHT countries that have this new toy now... the others all just show "coming soon" mode.
Here's what I think voice.yahoo.com leads to, first in those 8 countries, and then in any other country: (If I'm wrong, please advise!)