CDMA vs. GSM: What's the Difference? Two basic technologies in mobile phones, CDMA and GSM, represent a gap you can't cross. They're the reason you can't use older AT&T phones on Verizon's network and vice versa. But what does CDMA vs. GSM really mean for you?4g gsm desk phone CDMA (Code Division Multiple Access) and GSM (Global System for Mobiles) are shorthand for two older radio systems used in cell phones. In this story, I'll try to explain who uses which technology and what the real differences are. We first ran this story in 2012 and have updated it almost every year since. In 2019, we're getting close to the death date of these older technologies in the US. (Verizon is turning its CDMA off this year.) But millions of people are still using devices that require one or the other of these kinds of networks. When cell phone providers talk about a "G," they mean a generation of wireless technology. Each generation is able to support more users, and has better data transfer capabilities. The first generation was analog cellular phones. When carriers switched to 2G digital systems in the 1990s, they chose between several competing options; some of them died out, but CDMA and GSM are the two 2G camps that survived. They remained split during the '00s through the third generation of cellular, which added better data speeds but stayed incompatible.The CDMA/GSM split ended, in theory, as carriers all switched to LTE, a single, global 4G standard, starting in 2010. But because most phones still need to support 2G and 3G networks even to this day, you still see a difference in compatibility. The difference will remain in any phone that needs to access an older 2G or 3G network. Now carriers are starting to install 5G, which after a few false starts will be a single global standard called 5G-NR. But the CDMA/GSM split will still exist in any area where 2G or 3G networks are still alive.In the US, Verizon plans to turn off 2G and 3G at the end of 2019. T-Mobile will turn off 2G and 3G at the end of 2020. AT&T has already turned off 2G. AT&T and Sprint will keep 3G running until 2022.