Since the release of the iPhone, people have worked to get out of the locked shell the phone normally boots in. The principal reason behind this is to install and run software that Apple doesn't endorse or approve of, which given their rather draconian App Store entrance rules, is a considerable amount. At a convention with the Copyright Office, where a decision is to be made regarding DRM circumvention, the Electronic Frontier Foundation has been petitioning to make jailbreaking the iPhone an area that is "exempt" from any copyright law, letting people do it without worry. They are seeking to enable the execution of "lawfully obtained software" on any phone, regardless of what the manufacturer feels is OK to run. Apple does not agree.
In fact, they have come out to say that any circumvention of the software protection mechanisms on the iPhone, even doing it to your own for the purpose of running your own software, is an illegal copyright violation. Apple says that allowing the iPhone to be jailbroken will harm the creation of creative works for the platform. Even though that makes no sense, with any artificial restriction doing more to prevent development as opposed to encouraging it, Apple is dead set on convincing lawmakers and the world that allowing people to jailbreak the iPhone should be considered a crime and would result in the the platform suffering.
It's a very interesting debate, and clearly demonstrates how Apple truly feels about iPhone as a platform. The result of the meeting will have a big impact one way or the other, though I personally hope it swings in favor of the EFF. Do you feel that Apple is in the wrong by claiming that it is illegal to jailbreak a device you paid for?