They have applied for temporary testing authority to test new technologies in the 700, 800, AWS and PCS bands. Maybe using those to control their delivery drones?
http://www.fiercewireless.com/tech/amazon-seeks-sta-to-test-innovative-communications
Since those bands are currently occupied, is it one of those technologies that allows one's signal to piggyback on others carrier signal? There was a Florida company in the 2000's promising just that:
http://www.xgtechnology.com/products/