Okay, after downloading some books in Iceland, Amazon wont let you download any book and will ask you to contact their CS. I am from India and what I do is that whenever I see such a page, I ask a friend in US to download a book for me. Of course you will have to share your account details. This keeps me going for 4 or 5 more books and then I repeat the process.
Also, at work, we use a US proxyy, so Amazon sees me as a visitor from US itself and lets me download all the books I can. So, yeah, proxy will work. Cheers