Until recently, it was illegal to "unblock" cell phones in the United States. The U.S. Copyright Office has now sanctioned this process as legal as long as the user uses legal software. As a result of this new decision, there are now several options to remove a carrier block from your cell phone legally.
Request that your current cell phone provider remove the blocking from your cell phone as a courtesy, since it is legal in the United States.
Call your manufacturer or visit their website for the specific unblocking process for your cell phone model. Most manufacturers have a PUK or PIN Unblock Key that will unblock your cell phone.
Hire a reputable company that unblocks cell phones. Many of these companies actually have offices or kiosks that you can visit and have your cell phone unblocked on their premises. In other cases, the company may ask you to send your cell phone to them, and they will forward it back to you as an unblocked phone. In addition, some of these companies do have their own downloadable software for purchase on their site. Please see the references section of this article for a list of unblocking service providers.
Buy software that unblocks your cell phone. Please see the references section of this article for some choices of companies that provide an unblocking service. This software, in most instances, can be downloaded directly to your phone from an unblocking service provider's website. You will use your USB cable that is compatible with your cell phone.
Loss of data and functionality can occur if the cell phone is not unblocked properly, so proceed carefully. If you're uncomfortable about doing the unblocking process yourself, choose a reputable company to do it for you.