Cell Phone & SIM Card Compatibility

The most prevalent type of cell phone network worldwide in today's mobile phone market is the Global System for Mobiles standard. GSM networks use SIM cards to store contact data and to identify your phone to the phone carrier's network. Major GSM carriers in the U.S. include T-Mobile and AT&T. When switching phones on a GSM network, customers can visit a carrier's store and have data transferred from one SIM card to the other if the existing SIM card is incompatible with the new phone. Carriers typically offer SIM cards for free, although some might attempt to charge for a new SIM especially if there is no obvious need for the new card.

Code Division Multiple Access networks use older technologies and are less prevalent worldwide than GSM networks. Most notably, CDMA phones will not function at all in places like Europe or Australia. Non-LTE CDMA networks don't use SIM cards at all; rather they store contacts and other data ordinarily stored on a SIM card on the actual phone hardware itself and thus cannot be used on GSM networks. By extension, GSM phones cannot be used on CDMA networks. The major CDMA carriers are Verizon, Sprint, and MetroPCS.

Even if your existing phone uses SIM cards, you cannot be sure without some research whether your current SIM card is compatible with another phone. When 3G networks rolled out in the last few years, some users with 2G SIM cards had to upgrade their SIM cards to 3G-compatible cards to be able to get 3G speeds. Further, newer phones can use one of two SIM card sizes: Mini SIM cards, which are the standard, original size SIM cards, and Micro SIM cards, which are smaller than standard SIM cards. While there are cutting tools and/or instructions for cutting up existing SIM cards to a Micro SIM card size, cutting a SIM card isn't recommended as it may ruin either the SIM card itself or the SIM card slot in the phone.

As of November 2012, some CDMA carriers are moving with their Long-Term Evolution networks to using SIM cards. Verizon, for example, requires SIM cards for its 4G LTE network. While Verizon states that its 4G LTE SIM cards might be compatible on GSM networks, it also states that Verizon supports only Verizon-certified 4G LTE phones. For its part, Sprint has been moving to embedded SIM cards, panned by some reviewers because, since they are embedded into the phone, they cannot be transferred like normal SIM cards from one device to another. MetroPCS announced in late 2012 that it will be acquired by T-Mobile, and the latter company has said that it will move existing MetroPCS customers to T-Mobile's network by 2015.