They are trying to utilize the DMCA to prevent people from unlocking iPhones. But there is an exemption in the law for unlocking phones and the purpose of the DMCA was to protect copyrights, and cellular networks are not protected by copyright.
The reality is that they are trying to tie the two together. While that may seem like good business, it is questionable legally. I might suggest a Sherman antitrust attack on the tying, esp. given the lack of DMCA support for it.
Personally, I find the iPhone ridiculous. I may be going overboard from my bad experiences with a phone running Windows, but I just can't believe that I could easily make or answer calls on the ski slopes wearing gloves.