What is Code Division Multiple Access (CDMA)?


CDMA, which stands for Code Division Multiple Access, is a competing cell phone service technology to GSM, the world’s most widely used cell phone standard.

You've probably heard of these acronyms when being told that you can't use a certain phone on your mobile network because they're using different technologies that are not compatible with each other. For example, you may have an AT&T phone that can't be used on Verizon's network for this very reason.

The CDMA standard was originally designed by Qualcomm in the U.S. and is primarily used in the U.S. and portions of Asia by other carriers. 

Which Networks Are CDMA?

Of the five most popular mobile networks, here is a breakdown of which are CDMA and GSM:


  • Sprint
  • Verizon Wireless
  • Virgin Mobile


  • T-Mobile
  • AT&T

More Information on CDMA

CDMA uses a “spread-spectrum” technique whereby electromagnetic energy is spread to allow for a signal with a wider bandwidth. This allows multiple people on multiple cell phones to be “multiplexed” over the same channel to share a bandwidth of frequencies.

With CDMA technology, data and voice packets are separated using codes and then transmitted using a wide frequency range. Since more space is often allocated for data with CDMA, this standard became attractive for 3G high-speed mobile internet use.


Most users probably don't need to worry about which cell phone network they choose in terms of which technology is better.

However, there are some key differences that we'll look at here.


While CDMA and GSM compete head-on in terms of higher bandwidth speed, GSM has more complete global coverage due to roaming and international roaming contracts.

GSM technology tends to cover rural areas in the U.S. more completely than CDMA.

Over time, CDMA won out over less advanced TDMA (Time Division Multiple Access) technology, which was incorporated into more advanced GSM.

Device Compatibility and SIM Cards

It's really easy to swap phones on a GSM network versus CDMA. This is because GSM phones use removable SIM cards to store information about the user on the GSM network, while CDMA phones do not. Instead, CDMA networks use information on the carrier's server side to verify the same type of data that GSM phones have stored in their SIM cards.

This means that the SIM cards on GSM networks are interchangeable. For instance, if you're on the AT&T network, and therefore have an AT&T SIM card in your phone, you can remove it and put it into a different GSM phone, like a T-Mobile phone, to transfer all your subscription information over, including your phone number.

What this effectively does is lets you use a T-Mobile phone on the AT&T network.

Such an easy transition is simply not possible with most CDMA phones, even if they do have removable SIM cards. Instead, you typically need your carrier's permission to perform such a swap.

Since GSM and CDMA are incompatible with one another, you can't use a Sprint phone on a T-Mobile network, or a Verizon Wireless phone with AT&T.

The same goes for any other mix of device and carrier that you can make out of the CDMA and GSM list from above.

Tip: CDMA phones that use SIM cards do so either because the LTE standard requires it or because the phone has a SIM slot to accept foreign GSM networks. Those carriers, however, still use CDMA technology to store subscriber information.

Simultaneous Voice and Data Usage

Most CDMA networks do not allow voice and data transmissions at the same time. This is why you may get bombarded with emails and other internet notifications when you end a call from a CDMA network like Verizon. The data is basically on pause while you're on a phone call.

However, you'll notice that such a scenario works just fine when you're on a phone call within range of a wifi network because wifi, by definition, isn't using the carrier's network.

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