In locations such as the US where cell phone carriers either offer deeply discounted or free cell phones that have cell plans, these cell phones are usually locked in order to prevent them from working with other carriers. The carriers claim that this is required in order to subsidize the expense the cell phones. After some period of time, a carrier may agree to unlock the cell phone if requested to do so and may charge a fee. However, as a result of proprietary settings that are sometimes installed on the locked cell phones, they don’t always function properly with other cell phone carriers after they are unlocked.
As far as the consumer is concerned, this practice of carriers that lock cell phones and use proprietary settings defeats most of the advantages of SIM cell phones. The numerous complaints led to a class action lawsuit. Ideally cell phones need to be left unlocked, or at a minimum unlocked following the expiration of the initial contract.
One of the ways to get unlocked cell phones without the proprietary settings is to purchase them brand new from a third party vendor in its original, unlocked condition. The disadvantage of doing this is that the cost is usually near to the full retail cost. Many consumers may find it difficult to come up with the money necessary for a cell phone that they may be able to get for free with a plan. The advantage is that the third party cell phone that is unlocked should work equally well with any carrier that uses a SIM card.
Unlocked cell phones are in such demand that there are many third party services that will unlock cell phones for a fee. This doesn’t always guarantee that the unlocked cell phones will work properly, since the proprietary settings may remain. There are also numerous instructions that are available online to unlock cell phones, but a cell phone that is improperly unlocked may be rendered inoperable.
The carriers that use SIM cards operate on the GSM network. In the US, this includes T-Cell, AT& T Wireless, and Cingular Wireless. There are some carriers that use the competing CDMA network that don’t use cell phones that are enabled by a card. These carriers are Virgin cell, Verizon, and Sprint PCS. The CDMA is similar to a SIM card. In the future R-UIM cards will be utilized by the carriers.