GSM, CDMA, WCDMA? So confusing!

One of the biggest difficulties with purchasing phones for your prepaid carrier is compatibility.

Terms like GSM, CDMA, 4G, WCDMA will confuse your brain so much!

Well, take it easy and we will walk you through.

WCDMA – Wide Band Code Division Multiple Access (UMTS)

Before we talk about 4G or GSM. You must know WCDMA which stands for Wide Band Code Division Multiple Access. It is a third generation network developed by NTT Docomo and from 2G network CDMA. There are no cellular companies that are not based on WCDMA except Sprint (however they are slowly converting). WCDMA is a standard for 3G network. It was not a revolutionary upgrade to network, but by having the standard based on 2G GSM/EDGE. It was able for a simultaneous switch between GSM and EDGE. Also it was capable of compatibility with other UMTS family.

However, there are no phones that are  not WCDMA compatible. All carriers except U.S. Cellular and Sprint are based on WCDMA with all GSM phones compatible with WCDMA technology.

CDMA – Code Division Multiple Access

CDMA is a channel access method used by various radio communication technologies. It shouldnot be confused with the mobile phone standars called cdmaOne, CDMA 2000 (3G Evolution of cdmaOne) and WCDMA (the 3G standard used by GSM carriers) which are often referred to as simply CDMA, and use CDMA as an underlying channel access method.

One of the concepts in data communication is the idea of allowing several transmitters to send information simultaneously over a single communication channel.This allows several users to share a band of frequencies. This concept is Multiple Access or MA of CDMA. This is also why Verizon has much better pentration than AT&T or T-Mobile.

However, there is a disadvantage of CDMA. Your phone will not use a subscriber identification module to access cell towers. It will use an electric serial number to access. Which is why Verizon or Sprint’s phones usually don’t have a sim card. However, with WCDMA being deployed. All phones for all carriers have a sim. Still, if the phone does not have a GSM (2G) antenna, the (W)CDMA phone will not be compatible with GSM carriers.

GSM – Global System for Mobile Communications

Our world divides into four different generations of cellular network.

1G – Analog Cellular Network

2G – GSM or CDMA


4G – LTE, HSPA+ all based on WCDMA , Wi – Max

After the first generation network, carriers either chose GSM or CDMA standard for their 2G network. Both network are not compatible to each other. However, a WCDMA phone will be compatible with GSM network if it has a sim slot and has a GSM antenna.

GSM carrier frequencies are 900, 1800, 1900, and 2100 mHz. That is why iPhones are only capable with 2G network on T-Mobile’s network.

Phone Compatibility

GSM/CDMA compatible phone – iPhone 4S

GSM phone compatible carriers – AT&T, T-Mobile, Solavei (based on WCDMA and GSM)

GSM phone possibly compatible carruers – Verizon or Sprint if it is an iPhone 4S

CDMA only carriers-  U.S. Cellular and Sprint.

34 thoughts on “GSM, CDMA, WCDMA? So confusing!

  1. Appreciating the time and effort you put into your blog and detailed information you present.
    It’s great to come across a blog every once in a while that isn’t the same
    out of date rehashed material. Excellent read! I’ve saved your site and I’m including your RSS feeds to my Google

  2. Thanks for this information. Nowadays the world becomes very small because of these great searches of networks. This is really great development in the world of connectivity. Before many years people were using broadband, then they got wireless network and in 21st century we are using the all network types these are 2G, 3G and now 4G. You have mentioned details of GSm and WCDMA these are really informative to all users. Thanks you.

  3. i want to purchase htc desire 816. but i m confused that whether i can put a gsm sim in wcdma slot. plz reply me

  4. I am buying a WCDMA phone to use on a CDMA network. The phone is a Virgin Mobile phone that I want to use with Straight Talk. Will this work?

    1. To clarify for your question, CDMA based cell services do not have a SIM card. If your cellular provider provides you a SIM card, it should work fine. However, you may also want to check the bandwidth of the phone.

    1. Thank you for the question. You cannot change a SIM card from CDMA to WCDMA. First of all, CDMA smartphones or regular phones do not have a sim card. Also, the frequencies between CDMA and WCDMA are not a subject of comparison.

  5. I have a Samsung which ha
    s 2 undivided slot in its setting shows wcdma ,there I trying to use uim /CDMA SIM BUT it doesn’t show or not accepted ,why it is like this ?what could be the reasons ?thanks

  6. Hello,
    This post really helped me to understand difference.

    I have CDMA (TATA Indicom) and GSM (Idea) Sim Cards and would like to use in Redmi 3S Prime which has SIM Type: Dual Sim, WCDMA + LTE.

    CDMA (TATA Indicom) will work in WCDMA Sim slot?

  7. Loved the Article… very informative.
    I do have one question that I have failed to see if it was asked.
    I understand the difference in the bands used, and the compatibilities of individual phones for the most part… but if you had SIM cards from two separate companies say a pay as you go company that uses a HSPA+ and then another that was from a LTE SIM… Using a dual SIM phone would it be possible to have two separate numbers used on the same phone? Or would a phone need to be configured or built to use multiple bandwidths simultaneously?

    1. Hello Randall,

      Thank you for your comment. Regarding to bandwidth usage, the phone does not have to be specifically configured. As long as the phone can run two ‘working’ sim cards, the phone will automatically work out the network settings! Let me know if you have any more questions 🙂

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