It may be your device, but AT&T and Apple still owns the copyrights to the software that run the radios....
Apple also owns a whole bunch of rights relating to the hardware and the design of your iPhone.... This is absolute BS, which both the software industry and the media companies (with the backing of many bought and paid members of Congress) are trying to get the public to accept.
The main reason for the distinction between hardware and software is that hardware is governed by laws which are relatively firmed up and widely accepted. Software allowed corporations and their attorneys to spin a new concept in IP, with the aim of increasing profits by more efficiently milking the consumer. The publishers are trying to do exactly the same with ebooks.
You pay for the phone, it's yours to do as you please. You should be able able to legally jailbreak it, mod it, put pink and gold case on it, etc.. If any of these modifications cause a failure, Apple or the carrier may refuse to honor whatever warranty they provide, but that's about it.
DMCA is evil and only those directly benefiting from it, or complete dimwits, can honestly support it.