In the US, Verizon, US Cellular, and the old Sprint network (now owned by T-Mobile) 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 CDMA used for?

Code Division Multiple Access (CDMA) is a sort of multiplexing that facilitates various signals to occupy a single transmission channel. It optimizes the use of available bandwidth. The technology is commonly used in ultra-high-frequency (UHF) cellular telephone systems, bands ranging between the 800-MHz and 1.9-GHz.

Which country uses CDMA?

At this point in time, fewer than 18 percent of wireless networks around the world use CDMA technology. It is mostly found in the US within two of the four major wireless carriers, Sprint and Verizon Wireless. There are other countries that also use it, specifically Japan, South Korea and Russia.