Various types of cellular phones are made to function with a SIM card, also called a "subscriber identification module." This card is able to store all calling information about a person's cell phone subscription. All SIM cards are given to customers by their service provider and are able to give the customer access to calling others when the card is put inside of the cell phone.

When it comes to unlocked cell phones, they are able to connect with the SIM card of any cellular phone provider. On the other hand, if you have a "locked cell phone," you are limited to using certain types of phones that will only work properly with a certain provider. Many cell phone companies offer only certain phones so that they can maximize their profits by only offering phones that are manufactured by their company.

Most cell phone services in the United States of America do not usually allow the use of SIM cards. If you have gotten your cell phone service in the U.S., then you are probably familiar with the process of choosing a new phone for your plan; you will only be offered cellular phones that are made by the company that provides your calling service. There are certain carriers that allow people to get unlocked cell phones, but most of the time they do not allow it. Why wouldn't they let more people have their cell phones unlocked? Mostly due to the fact that they want to make sure that their customers are not buying phones through another provider.

A lot of people are very unhappy that they are not given the freedom of getting any phone with their provider. With that said, the provider of the cell phone contract that you have is in full control of your phone options. This means that not everyone can go out and get themselves an iPhone to use with any service provider.

Some people still feel jeopardized by the fact that unlocked cell phones are not offered at most major retailers in the United States. There have been cases where people have purchases unlocked phones on the internet or from private sellers, but most of them have a tough time configuring it to work properly in correspondence with their policy.

The whole trick is finding a cell phone company that allows the use of SIM cards in their plans. In non-U.S. countries, unlocked cell phones are fairly popular. This gives people the opportunity to use whatever kind of phone they want as long as it has a SIM card. There have been individuals in the United States that have been able to make significant tweaks and changes to their phone in order to "unlock it," but the process is usually very intricate and detailed.

All GSM cell phones' service providers allow the usage of SIM cards. This means that if you are affiliated with T-Mobile, AT&T, or Cingular, you will be able to get a phone that can be unlocked. All other carriers, which are considered "CDMA phone providers," do not allow phones to be unlocked.