There are always questions from people who are looking to switch wireless services but want to take their existing phones with them.

While it is possible in most cases, in order to do so, you have to have a good understanding of the various cellular technologies that are out there.

In this article, we will talk about these wireless technologies, i.e. CDMA, GSM and LTE.

GSM (3G)

GSM means Global System for Mobile communications. Along with most mobile operators throughout the world, there are two wireless carriers in the United States that use GSM as a backbone.

They are AT&T and T-mobile US. On a GSM network, a user’s phone number and their text and data plans are programmed into a small chip called a SIM Card or Subscriber Identity Module.

Since your wireless service is only tied to the SIM Card with GSM, you can easily move your service to a new phone optimized for the same cellular service just by inserting your SIM Card into a new device.

This is helpful if your existing device gets damaged or if you want to travel internationally with an unlocked phone.


CDMA means Code Division Multiple Access. CDMA was created by Qualcomm (the same company that made CPUs for an overwhelming majority of android windows phones sold in the United States).

For those who live in the United States, Verizon Wireless and Sprint are the two carriers that runoff on CDMA as a backbone. Now the key thing that makes CDMA different from GSM is that CDMA does not involve the use of SIM Cards.

Instead, for CDMA carriers like Verizon or Sprint, each carrier will have a list of codes called ESNs (Electronic Serial Numbers). This list identifies particular handsets that can be used on a given CDMA network.

If your phone does not have a code that is listed on a given carrie’s network, you simply cannot use that device on a carrier like Verizon or Sprint.

So overall, instead of embedding your subscriber information unto a SIM Card, with the CDMA-based carrier, your voice plan, your texting plan and your data plan is all embedded in the actual phone.

Differences between CDMA and GSM

GSM allows you to move your service from one device to another through the simple use of a SIM Card.CDMA carriers have their networks embedded into their devices.
GSM devices can transmit voice calls and use data at the same time.CDMA devices cannot transmit voice calls and use data at the same time


Some people use a Verizon or Sprint phone, but these phones have SIM Cards. It is most likely because you are using an LTE 4G enabled device.

All four of the national United States carriers have been expanding their LTE for the past few years. LTE means Long Term Evolution Network.

The reason why you here carriers talk about LTE so much is because LTE is the fastest cellular data connectivity that is available right now. If you are on these carriers and your phone disconnects from the LTE network, your phone will use CDMA as a fallback.

Over the past several years, most smartphones have had both a voice connection and a data connection built in. More recently, you may have heard of Voice-Over LTE.

Voice-Over LTE is basically an occurrence where your network processes both data and phone calls over the same connection instead of separately. This benefits CDMA LTE base customers in the sense that those folks can now talk to other people and use data at the same time.

Other Networks

Between 3G and 4G GSM carriers like AT&T and T-mobile, there is a technology called HSPA (High Speed Packet Access). It is sort of like 3.5G. In terms of speed, it provides about 21megabits per second.

If your network carrier speed is really truncated, you might see an E next to your signal bars, if you have a GSM device. It stands for Informative 2G or Edge.

2G brought the ability to access the internet over cellular as well as first modern smartphones like the Blackberry and the first iPhone. For CDMA devices, you may see a form of 2G called 1x displayed on your device.

Overall, GSM and LTE are the most common forms of connectivity used today, along with CDMA in the United States and a handful of other countries.

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