Isn't this the same model that funds most websites? Zero cost in exchange for advertising and, I'm guessing, giving up your private information - with all the positives and negatives associated with that model. I'm too lazy to check: Does Amazon say what private info is collected? Info on phones can be much more personal and more accessible to other applications.
http://www.amazon.com/Amazon-com-Amazon-Underground/dp/B004G...
Thanks to mkaziz above for the link, apologies for the repetition