CDMA in the United States

''Many users asked why major operators in the US like Verizon and Sprint have not being mentioned in our survey. This is explained in the Guidelines and the beginning of United States chapter again. It is assumed that you are carrying a GSM-based device and want to use it in the US. But for various reasons, this exclusion seems now outdated. Still, it may confuse many readers when CDMA is now shown on the same list as most incompatibilities still exist. Unlike China or Japan, where we started to list CDMA providers, the US list is already rather long and will become even less navigable adding CDMA. Furthermore, it still appeals to a very limited audience why you may be interested in a CDMA prepaid SIM card. That's why this segment has been outsourced and gathered in a new article. This page is a breach of the guidelines that say "GSM-only", but for some reasons it makes sense:''
 * We've never ignored the market leader in any country. Undoubtely, Verizon's LTE has the best coverage nationwide and the most customers within the country.
 * You may be coming from Japan, China or Canada and have a CDMA-device that you want to use in the US. 95% of the countries worldwide are on GSM only, but there is the odd chance.
 * The barriers between both system lines are slowly narrowing. 4G/LTE is being used by both GSM and CDMA.
 * Not having a CDMA-device, you can still think of buying one to get the supreme speeds and coverage of Verizon in the US.

Basics
Until 4G/LTE has arrived, the cellular world in the US was split into two systems, that were not compatible. CDMA technology is used in only a few countries of the world. But in the US it is employed by major operators like Verizon and Sprint. You could easily identify it by the non-existing SIM card. The device was electronically registered or “married” with the provider and you couldn’t change that. You could only buy a Verizon/Sprint phone or modem but you could use it only on their own network and nowhere else.

The adoption and implementation of 4G/LTE changed the game. Now, both CDMA- and GSM-providers use the same technology and often even the same frequencies for wireless transmission. CDMA-devices now have SIM cards too and they fit in the same sized-slots like GSM SIMs. This is the reason why users are starting to think of crossing the barriers.

Opening up of CDMA
The CDMA providers had to react first as their system was clearly on the loosing side. Their devices could not be used at all abroad, not even on roaming as 95% of all countries are still on GSM-only. This was a big loss of revenue too. That's why they agreed to adopt the USIM-system for 4G/LTE giving high-class CDMA devices for the first time access to GSM networks. These devices are now labeled as "world phones" meaning they can roam on every network with which the home provider has contracts.

Opening up of GSM
Unfortunately, the opening up of GSM towards CDMA progressed much slower. There was no pressure to enter new markets as every country has at least one GSM provider. This is why it's still tricky to use a GSM device on Verizon and impossible on Sprint, as it's shown below.

Verizon
Verizon is the largest wireless service provider in the US. For 2G their CDMA uses an own system, as well as for 3G that is called EVDO and both are totally incompatible with GSM.

In 4G/LTE it has the best coverage, highest speed and most reliable network in the country (4G/LTE coverage map and comparision with its rivals: HERE). While AT&T covers almost 300 million and T-Mobile 250 million in 2015, Verizon covers more than 305 million or 98% of the US population.

Verizon's LTE mainly uses 700 MHz (band 13) with supplemental coverage on 1700 MHz (AWS band 4) that are frequencies used by AT&T and T-Mobile too.