Cell phone Glossary: What Is GSM vs. EDGE vs. CDMA vs. TDMA?

These standards are the reason some phones can't switch networks

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While selecting the right mobile phone service plan at your carrier of choice is important, so is choosing the right carrier in the first place. The type of technology the carrier uses (GSM, EDGE, CDMA or TDMA) matters when you buy or sell a cell phone.

GSM vs. CDMA

For years, the two major types of mobile phone technologies, CDMA and GSM, have been incompatible competitors. This incompatibility is the reason many AT&T phones won't work with Verizon service and vice versa.

  • GSM network providers put customer information on a removable SIM card. This approach makes it easy to switch phones; you just take the SIM card out of your old phone and insert it into your new one. GSM technology is widespread in Europe. Combine that fact with a phone with a removable SIM, and you have a phone you can use on overseas visits with just a SIM change.
  • CDMA phones may or may not have SIM cards, but the user information is stored with the service provider, which must give its permission for you to switch phones. CDMA phones must be programmed with every carrier you use. Whenever you switch carriers, the phone must be reprogrammed for that carrier, even if it is an unlocked phone.

Network Technology Effect on Quality

The quality of the phone service has nothing to do with the technology the provider uses. Quality depends on the network itself and how the provider structures it. There are both good and not-so-good networks with GSM and CDMA technology. You are more likely to run into quality concerns with smaller networks than with the big ones.

What About Unlocked Phones?

Since 2015, all U.S. carriers have been required to unlock their customer's phones after they fulfill their contract. Even if you decide to have your phone unlocked or to buy a new unlocked phone, it is either a GSM or CDMA phone at heart, and you can only use it with compatible service providers. However, having an unlocked phone gives you are a wider range of service providers to pick from. You aren't limited to just one.

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What Is GSM?

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The Global System for Mobile Communications standard is the world’s most widely used cell phone technology, popular in both the U.S. and internationally. Cell phone carriers T-Mobile and AT&T, along with many smaller cellular providers, use GSM for their networks.

GSM is the most popular cellular technology in the U.S., but it is even bigger in other countries. China, Russia, and India all have more GSM phone users than the U.S. It is common for GSM networks to have roaming arrangements with foreign countries, which means GSM phones are good choices for overseas travelers.

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What Is EDGE?

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Enhanced Data Rates for GSM Evolution is three times faster than GSM and is built upon GSM. It is designed to accommodate streaming media on mobile devices. AT&T and T-Mobile have EDGE networks.

Other names for EDGE technology include Enhanced GPRS, IMT Single Carrier and Enhanced Data Rates for Global Evolution. 

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What Is CDMA?

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Code Division Multiple Access competes with GSM. Sprint, Virgin Mobile, and Verizon Wireless use the CDMA technology standard in the U.S, as do other smaller cellular providers.

When 3G CDMA networks, also known as "Evolution Data Optimized" or "EV-DO" networks, first rolled out, they couldn't transmit data and make voice calls at the same time. In most cases, particularly with cellular providers with a 4G LTE network, that problem has been successfully addressed.

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What Is TDMA?

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Time Division Multiple Access, which predates the more advanced GSM technology standard, has been incorporated into GSM. TDMA, which was a 2G system, is no longer in use by the major U.S. cell phone service carriers.