Code Division Multiple Access (CDMA) and Global System for Mobile Communications (GSM) are different types of mobile phone networks and forms of technology. Both CDMA and GSM mobile phones and networks are prevalent in North America and nearly every other region in the world. There is more than one method to check, or determine, which network your mobile phone belongs to. You can determine if a network is CDMA or GSM based on the wireless service provider you use or by inspecting the physical characteristics of your mobile phone.
Determine if your phone requires a Subscriber Identity Module (SIM) card. A SIM card is a small, removable card or chip that contains your mobile account information and is interchangeable between all GSM phones.If you use a SIM card in your mobile phone, the phone is a GSM device; otherwise, if your phone does not require the use of a SIM card, the phone is a CDMA device.
Check the inside of your phone for a SIM card. This step can be performed if you are unsure if the phone requires the use of a SIM card.Open the battery compartment of the phone. The SIM card holder is normally located underneath the battery; however, some mobile phones will have a SIM card slot or tray located on the outside of the phone.
If you need assistance with locating the SIM card slot, or determining if the phone requires the use of a SIM card, consult with your phone's manual or contact the manufacturer of the phone.
If you use an iPhone 4, the GSM model will contain a SIM card tray on the right side of the device; whereas the CDMA model will not have a SIM card tray.