In the US, Sprint, Verizon and US Cellular use CDMA. AT&T and TM cell phones use GSM. The rest of the world uses GSM. The worldwide spread of GSM occurred because Europe enacted the technology by law in 1987 and GSM was born from an industrial consortium.
Firstly, neither GSM nor CDMA are technically better, they ultimately offer the same service and the quality of a network depends on the operator, not the cellular standard used. Secondly, GSM phones can be unlocked and operators can be changed, while CDMA phones can be locked by an operator.
Unlike CDMA phones, GSM phones have a SIM card slot. In other words, CDMA is a portable device-based standard in which a telephone number is associated with a particular device. To switch to another phone, contact your network operator, deactivate the old device and activate the new one.
TMobile and AT&T work on GSM networks. Sprint and Verizon use CDMA technology. The general rule is that a CDMA phone will not work on a GSM network and vice versa, it will work on different frequencies. However, most new iPhones like 8 and 8 Plus and some Google Nexus phones can work with both technologies.
MetroPCS is a GSM / LTE / VoLTE operator. They were originally a CDMA operator until TMobile bought them and they switched to the TMobile network. You might be surprised to learn that MetroPCS was the FIRST operator in America to offer LTE and VoLTE.
Verizon already has GSM as its main network. As of January 1, 2020, CDMA OR SELF-FONCTION will no longer be supported on the Verizon network. If you have a CDMA device now, you can save for a new phone as it will stop working after next year.
A GSM operator does not care which phone has a SIM card. For this reason, a CDMA network is not required to lock phones. So in this case every CDMA phone will be unlocked, but it doesn’t matter because the lock is done on the support site.
LTE (Long Term Evolution) is a broadband radio technology for high speed data communication for mobile phones. The main difference between the technologies is that CDMA and GSM can support cellular and data, while LTE can only support data. The GSM phone had a SIM card slot, the CDMA phone did not.
Well, GSM networks like US Mobile, TMobile and AT&T use removable SIM cards. This means that unlocked phones from other US GSM operators will work on the US cellular network. Verizon and Sprint, on the other hand, are CDMA operators. CDMA operators do not use SIM cards and most CDMA phones are network locked.
Frequencies and carrier bands
In the US, Sprint, Verizon, and US Cellular all use CDMA. AT&T and TM cell phones use GSM. The rest of the world uses GSM.
Moto G4 Plus, Motorola Droid Turbo 2 and Moto X Pure can work on GSM and CDMA networks. These phones are also known for their contactless operation. For example, turn off the LED flashlight by lowering the phone twice.
The easiest way to unlock your device is to call your carrier and ask for a Network Unlock Code (NUC). Most will give you one, and some will even give you one for free when the contract expires. Once you receive the code, you should be able to enter it into your phone to unlock it.
All mobile phones are designed to provide the service with a SIM card. With an unlocked device, a GSM smartphone can be processed and used in a different network by removing the old SIM card and inserting a new one from the new operator. EVDO is the 3G technology used in CDMA networks.
In order for the unlocked phone to work with Verizon, Verizon hardware called SIM card is required. The SIM card is a memory card and a processing chip specific to each network. Contact Verizon with the make and model of the unlocked phone to get the appropriate SIM card.
TMobile claims the second best network and coverage in the United States, narrowly beating AT&T in third place. Neither AT&T nor TMobile are the cheapest, but they both offer a good selection of feature-rich plans, especially unlimited data plans.
Before unlocking your TM device
It is technically possible to use a Sprint phone in the TMobile or AT&T GSM network if the device is LTE compatible or an iPhone. However, you can still use the phone on a Sprint MVNO such as Ting, Boost Mobile, or Republic Wireless.