Now that Vodafone Germany's international SIM, mobi, has had a month or two to straighten out its website, it appears that it does not offer any cheap calls to the US, Canada, Australia, New Zealand, or the pre-2005 EU countries (except for Greece, which I guess counts as a "guestworker country"). Of other rich countries that Blauworld can call cheaply, Japan is included but South Korea is not. It looks a little like the original Blauworld pricelist. However, I don't see any good reason why anyone would take mobi instead of Blauworld; Vodafone Passport would be one, but it's largely of interest for people travelling to the countries that are not included.
http://www.mobi-online.info/tarife.html#01