Trustive has released a fascinating worldwide connectivity plan that charges per MB for 3G and per minute for Wi-Fi: I've seen variants of this before, but I believe Trustive has the only service with this scope.
It works this way: you sign up for €99, which includes a €54 credit for service and a Trustive SIM card. If you don't have an unlocked USB 3G modem, Trustive offers one for €150. There's a €15 shipping fee, too. Trustive confirmed that shipping covers international transit.
With that in hand, you can connect to Wi-Fi and 3G network in over 70 countries (Trustive provides a list). All Wi-Fi access is billed at 9 euro cents (€0.09) per minute, with no minimum, regardless of data transferred.
3G use is tiered: Zone A countries, which include the United States, most European nations, India, and China (but not Canada or Mexico), cost €1.50 per MB. Zone B countries are a whopping €15 per MB.
Trustive has some bugs to work out in its explanation, however. The USA, Canada and other countries appear in both Zone A and Zone B lists with no explanation. And there are typos and some confusing information around the site.
The prices are extraordinarily steep, but in the universe of international roaming, may appear perfectly reasonable.