Tim Wu has a great article chronicling his decision to unlock his iPhone (which allows him to use it with carriers other than AT&T and run applications not authorized by Apple). He then considers the legal and ethical implications of his actions:
Did I do anything wrong? When you buy an iPhone, Apple might argue that you've made an implicit promise to become an AT&T customer. But I did no such thing. I told the employees at the Apple Store that I wanted to unlock it, and at no stage of the purchasing process did I explicitly agree to be an AT&T customer. There was no sneakiness; I just did something they didn't like.
Meanwhile, lest we forget, I did just throw down more than $400 for this little toy. I'm no property-rights freak, but that iPhone is now my personal property, and that ought to stand for something. General Motors advises its customers to use "genuine parts," but it can't force you to buy gas from Exxon. Honda probably hates it when you put some crazy spoiler on your Civic, but no one says it's illegal or wrong.
The worst thing that you can say about me is that I've messed with Apple's right to run its business exactly the way it wants. But to my mind, that's not a right you get in the free market or in our legal system. Instead, Apple is facing trade-offs rightly beyond its control. When people unlock phones, Apple loses revenue it was hoping for, but also gains customers who would have never bought an iPhone in the first place. That's life.
This is exactly right. Apple, it should be emphasized, was entirely within its rights to sign a contract promising that the iPhone would only be sold in conjunction with AT&T's wireless service. But that contract binds Apple and AT&T; it doesn't bind Apple's customers. Absent any explicit contractual agreement, customers are under no legal or moral obligation to use their iPhones only in the ways Steve Jobs wants them to. Hence, unlocking your iPhone is, as Wu puts it, "legal, ethical, and just plain fun."
It's also worth highlighting that part of the reason Wu concludes that unlocking the iPhone is legal is that the Copyright Office included cell phone unlocking as one of its explicit exemptions to the Digital Millennium Copyright Act, the law that I've argued is holding back innovation in other parts of the consumer electronics industry. It's great that the Copyright Office has recognized that using your iPhone with the carrier of your choice has nothing to do with copyright infringement, but it's still not legal to (for example) build a DVD player that will fast-forward through commercials, or to build an MP3 player that will play songs purchased from iTunes. It would be better if the DMCA's anti-circumvention provisions were repealed, so that inventors didn't have to go begging to the bureaucrats at the Copyright Office for permission to engage in this kind of beneficial tinkering.