If this is for the US, the most interesting question is will Amazon offer their own cellular service? Walmart is doing this with their "no contract" plans (
Walmart Offering $45 Unlimited Cellphone Plan Nationwide). The phone might be primarily for Europe, where branded phones sold without a SIM make more sense (or Amazon could bundle service). Amazon has cellular service bundling experience world-wide from their Kindle 3G sales, but that experience may also tell them that getting phone companies to innovate is hard.