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Telecom Courses : Differnece between GSM and CDMA

Tutorial by:      Date: 2016-08-06 04:16:22

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Two basic technologies in mobile phones, CDMA and GSM represent a gap you can't cross. They're the reason you can't use many AT&T phones on Verizon's network and vice versa. But what does CDMA vs. GSM really mean for you? 

CDMA (Code Division Multiple Access) and GSM (Global System for Mobiles) are shorthand for the two major radio systems used in cell phones. Both acronyms tend to group together a bunch of technologies run by the same entities. In this story, I'll try to explain who uses which technology and what the real differences are.


Which Carriers are CDMA? Which are GSM?

In the U.S., Sprint, Verizon and U.S. Cellular use CDMA. AT&T and T-Mobile use GSM.


Most of the rest of the world uses GSM. The global spread of GSM came about because in 1987, Europe mandated the technology by law, and because GSM comes from an industry consortium. What we call CDMA, by and large, is owned by chipmaker Qualcomm. This made it less expensive for third parties to build GSM equipment.

There are several variants and options carriers can choose, like toppings on their technological ice cream. In this story we'll focus on U.S. networks.


While most cell phones users are not aware that there is even a difference between wireless technologies,CDMA cell phones and GSM cell phones are very different. For the most part, buyers have chosen a wireless network technology without even realizing they have done so. This is because every wireless network provider uses one or the other.

Any buyer who has ever wondered why they can't simply use a phone that was created for AT and T on a Verizon network and vice versa should know that the differences between CDMA and GSM technologies are the sole determining factor behind this. In effect, the two technologies represent different kinds of radio systems.

What is CDMA?

CDMA stands for Code Division Multiple Access. CDMA does not specifically refer to one kind of technology or one network, but for a system of networks that have evolved over time. Each successive version of this network has sought to provide better, faster network access with a larger amount of coverage.

One of the notable things about CDMA technology is that it is the primary type of technology used for cell phones and smartphones in the United States. Cell phone providers that use CDMA technology include Verizon,Sprint, and US Cellular.

This means that for the most part, in the United States CMDA networks have seen more growth, and are likely to provide a much better user experience in terms of the amount of coverage a cell phone is able to receive within the United States. In addition, data might be more accessible, and users may be less likely to experience issues such as dropped calls, depending on the cell phone and the network provider they are using. One of the downsides is that using a CDMA network makes it much more difficult to switch out phones between networks.

What is GSM?

GSM, or Global System for Mobile, is the primary type of technology used for cell phones in the rest of the world. Within the United States, a much small number of network service providers are on the GSM standard, among themT-Mobile and AT and T. That means the amount of coverage an individual may receive when using a GSM-compliant phone may be much more limited.

However, using a GSM-compliant phone also makes it much easier for a user to switch providers or networks, as all that they must do in order to make a switch is purchase a new SIM card for their device. The interchangeability of GSM cell phones, as well as the ability to easily switch between networks, makes them a much more appealing option for international travelers who plan to switch between different networks when on trips to countries that primarily use GSM technology.

This is especially important for those who take frequent trips to Europe. Europe adopted GSM technology in the 1980s and has been on this standard ever since. As the technology is required of network providers by law, users will not find access to CDMA networks in any countries within Europe.

Notable Difference Between CDMA and GSM Technologies

There are many differences between these technologies, and keeping track of them can be a challenge. Any individual who is looking for better usage out of their cell phone and their network provider to have a good understanding of what these differences are, and what they should look out for when choosing a new smartphone device or cell phone.


GSM Technology

CDMA Technology

Type of Storage Used

SIM Card

Internal Memory

Network Service

Dictated by the user's SIM card.

Dictated by the user's device.

International Roaming

Easier access

More difficult access

Frequency Band

Multiple (850, 900, 1800, and 1900 MHz)

Single (850 MHz)

Data Transfer



Questions to Ask Before Choosing CDMA or GSM Technology

There are a number of reasons why a cell phone or smartphone user would choose between one or the other when purchasing a new device or thinking about signing up with a new network. For the average user, the differences will not be all that noticeable. An individual who will be purchasing a phone for long-term use, who does not travel often or otherwise has no special needs when it comes to their phone, is much better off simply choosing a plan that works well for their needs and that has a record of good service in their area, regardless of whether it is GSM or CDMA compliant.

That being said, there are also a number of factors that may play a big role in a buyer's decision between the two. There are a number of questions an individual might choose to ask before making a choice.

  • Will they be traveling with the device?
  • Do they change cell phones or smartphones on a regular basis?
  • Do they have multiple cell phones or smartphones they would like to use with the plan?

Identifying a CDMA or GSM Phone

On first inspection, it might seem like a simple enough process to determine whether a cell phone is CDMA or GSM compliant. After all, only a GSM phone supports a SIM card, correct? That is not necessarily the case - at least, not anymore. CDMA cell phone providers still do use SIM cards - however, they are different from those used for GSM devices.

In this case, the SIM cards used are for the 4G LTE networks used by the companies. It is important to keep this in mind, especially with cell phones made for companies such as Sprint and Verizon, as the presence of a SIM card may trick some buyers into thinking they will be able to use the SIM card from their old device in their new device, when this might not be the case. The only true way to determine whether a cell phone is for a CDMA or GSM network is by determining the network the phone was originally made for or, if purchasing a cell phone or smartphone on a site such as eBay, by thoroughly reading the product listing to ensure that the phone is on the network of the individual's choice.

What CDMA and GSM Mean for Unlocked Phones

One big question a lot of buyers have is what the differences between CDMA and GSM technologies mean when they want to purchase an unlocked phone. Typically, even after being unlocked a CDMA phone will only work on the CDMA network, and a GSM phone will only work when used with a GSM provider.

However, there have been some advances in the cell phone and smartphone industry that have grayed the lines between the two types of technology. While a GSM phone will still be unable to work on a CDMA network regardless of whether or not it has been unlocked, a number of CDMA phones are now coming with the option of being unlocked and made usable on GSM networks.

This is good news for those buyers who prefer using CDSM phones in the United States but who are in need of a GSM-compliant phone for travel to other parts of the world. Additionally, it expands the options for buying unlocked phones, whether they are used or new.

Buying CDMA or GSM Cell Phones

The easiest way of finding a GSM- or CDMA-compliant phone is to simply search by this categorization. Have in mind the type of phone you are interested in purchasing - for example, a Samsung Galaxy - and include the search term "GSM" or "CDMA" in the eBay search box as you begin. If this search does not turn up the results you want, you may then consider searching by the specific network provider, such as Sprint or Verizon, keeping in mind the network the provider is on.

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