Not going into the legal arguments (from a moral standpoint, I am paying Amazon for the content, so I think what I do with that content within my own home should be sacrosanct) but I was able to purchase content from the Amazon Kindle store by registering my iPhone, and then was able to get the content onto my Sony Reader. Full description is here:
https://www.mobileread.com/forums/sho...&postcount=142