A few of our European readers might have discovered this already, but Google's Carrier Billing page for the Play Store was updated yesterday. According to the additions, Android users on the Bouygues carrier in France and Play (the carrier, not the store) in Poland should now be able to buy apps and media via their phone bill. We've reached out to Google for confirmation and haven't heard back, but a post to this list is usually conclusive.
Bouygues is the second carrier in France to support Play Store billing, behind SFR, while Play is the first in Poland to allow it. Both the French carriers allow payment in Euros, while Polish customers use the regional Zlotys currency. French and Polish readers, feel free to sound off on your experiences in the comments - the feature may be rolling out in incremental regional updates to the Play Store app.
While carrier billing is supported on the Big Four cellular providers here in the United States, Google still has a long way to go in the rest of the world. Only nine countries in Europe have access to carrier billing, and most have it only on one or two carriers.
Update: Google has confirmed the updated carrier billing availability.
Source: Google Play Store support