Peter wants to know how he can unlock his phone and use it with another carrier. Leo says that according to the Library of Congress, you could legally unlock your phone and swap carriers. Carriers are starting to unlock phones if you've been a member in good standing and your contract is up. But they also will unlock it if you're traveling out of the country. This is largely due to the subsidizing of your phone by your carrier, which is why you pay so little for it. But the trend is now moving towards a month to month model where people will pay full price for their phones and get a lower cell phone bill.
But there are ways Peter can unlock his phone himself through software, or by rooting his phone. He should check out XDA-Developer Forums. But if he just asks his carrier, chances are they'll do it. Some even sell their phones unlocked out of the box. If the carrier has been absorbed, he could try an independent cell phone provider.
Peter can also search for "unlock carrier lock" with his phone model. But he should be careful as some models, like Samsung, make it very hard to unlock the phone. Motorola, on the other hand, is pretty easy to unlock.