Well, here are the results of my findings:
- Vonage: only USA, Mexico, Canada and UK
- AT&T: there seems to be an unbelievable service establishment charge of 1,500$ for their GIS service; I asked them on a an online form whether that was really applicable, but they did not reply to my enquiry; there is no email address, postal address or fax number on their website (not sure if I want to commit myself with a company like that

)
- MCI (Worldcom): replied that they don't provide this service
At this stage, I found a small Polish telecom company specialized in VOIP that offered me a virtual classic (not VOIP) local number in Poland, diverted to the US, for ca 10$ a month + tolls. Great; that was the type of offer I wanted.
I still need to find a similar service in Italy and Germany.
For Germany, there is the offer of kall8international.com , but when I actually tried to subscribe, until 2 days ago I got the following message:
The international numbers highlighted above are provided by a third party carrier. We have been experiencing some problems with the quality of these numbers and the carrier is in the process of upgrading their network to address these issues. If these issues are not resolved within the next two months, we might be forced to discontinue the international portion of our service. If you want to go ahead and sign up for these numbers now, please let us know if you experience any problems - your feedback on this situation would be very helpful.
That message has disappeared today, but I am a bit worried to commit myself too, although I do know that kall8 is a serious company. Also, it is not precisely cheap, with setup at 50$ and monthly fee at 28$ per number.
So, still looking.
Any other ideas?