Holiday Phone (www.holidayphone.com) and 40% off? Have you heard of it?
 

Hotels.com offers this provider and a 40% discount if you have a US address. When you book certain hotels. Though I did not manage to hop on to the SIM discount page from the hotel booking, it must be a problem on their site or on my part.

Anyways, don't you hate SIM cards where you can't openly see all tariffs in one place? For example I have no idea how to see the tariffs on this one. Go to the Destinations & tariffs tab and? Nothing. Not to mention what if you want to go to a country not covered by them.