How Do I Unlock My Cell Phone or Smartphone?

The question you should be asking is: "Can I Unlock My Cell Phone or Smartphone?"
The answer: Maybe. Some smartphones and cell phones can be unlocked, but it typically requires help. Once you've purchased a locked phone, it's in the carrier's best interest to keep that phone tied to their network, so they're going to make unlocking it pretty difficult.
Some phones can be unlocked by modifying their software, while others require an alteration to their hardware. You can ask your carrier about unlocking your phone, but it's not likely that they'll do it--especially if you're still under contract. Alternatively, you can pay a third party to unlock your phone for you, but remember that if your phone is damaged, you’re not likely to get any help fixing it. Unlocking it probably voids any warranty you may have.
And remember that it may not make sense for you to unlock your phone until your service contract has expired, anyway. You'll either be forced to pay a monthly fee for the remainder of your contract, or you'll have to pay a termination fee to break your contract.