jkOnTheRun's piece:
Verizon Wireless jumping in the femtocell pool drew my attention to femtocells. These are small cellular "towers" for in home use, that send voice traffic over your existing broadband connection.
Sprint's AIRAVE deployment, though limited, is further along than Verizon. This is mostly for voice, so AIRAVE probably does not work with the Kindle's WhisperNet. In any case, the obvious alternative would be to add WiFi to cell phones and (particularly) to data-centric devices like the Kindle.