PrevNEXT

How to Unlock a Cellphone or Smartphone

By: Ed Grabianowski & Talon Homer  | 

Cellphone Unlocking: Can Your Phone Be Unlocked?

two SIM cards in phone
Each phone company has its own SIM card. You can switch out the card to use another cellphone company. Some phones even have space for two SIM cards, useful if you do a lot of international travel. Madiha Ali/Getty Images

There used to be two cellphone technologies that were used by the majority of the world's mobile phone service providers: Global System for Mobile communication (GSM) and Code Division Multiple Access (CDMA). If you had a CDMA phone, then your phone was unlockable. However, if your phone operated on a GSM network, then it might be unlockable.

What's the difference? GSM phones used subscriber identity module (SIM) cards. A SIM card is a small card that's inserted into the phone. It contains all your contacts and settings, and it's linked to your account. You could take the SIM card out, put it into another phone, and if someone called your number, the new phone would ring. You could also put a different SIM card in your unlocked phone, and your phone would then work with whatever phone number and account was linked to that card. CDMA phones had no SIM cards and needed to be authenticated by the service provider, which made unlocking a phone impossible.

Advertisement

If a phone was locked, the service provider installed some software on the phone that tied the subscriber ID number on the SIM card to the serial number of that particular phone. If the SIM card and phone serial number didn't match, the phone simply wouldn't work. The SIM card wouldn't work in other phones, and the phone wouldn't work with other SIM cards.

If you lived in North America, you could usually determine whether your phone is GSM or CDMA based on the service provider you used. T-Mobile and AT&T used GSM, while Verizon and Sprint used CDMA. In Europe, almost all phones were GSM.

Currently CDMA is kept around mostly for legacy devices, while GSM has evolved into 4G LTE and 5G. Old 3G GSM networks are also being phased out in the coming years. Almost any phone now should be compatible with SIM cards.

ElectronicsCell PhonesHow Cell Phones WorkElectronicsCell PhonesCan cell phones make you sterile?ElectronicsCell PhonesCell Phone PicturesElectronicsCell PhonesHow Cell Phone Jammers WorkElectronicsCell PhonesWhich cell phone should I buy for my grandmother?ElectronicsCell PhonesInside a Cell PhoneElectronicsTravel GadgetsIntroduction to Global Cell PhonesElectronicsCell PhonesHow are cell phones cloned?ElectronicsCell PhonesHow Prepaid Cell Phones WorkElectronicsCell PhonesCan you charge your cell phone with a fuel cell?ElectronicsCell PhonesTop 5 Future Cell PhonesElectronicsCell PhonesHow do I use my cell phone as a modem?ElectronicsCell PhonesIntroduction to How Video Conferencing Cell Phones WorkElectronicsCell Phones5 Ways to Donate Your Old Smartphone or Cell Phone to CharityElectronicsCell PhonesCell Phone Tower PicturesElectronicsCell PhonesHow Much Radiation Does Your Cell Phone Emit?ElectronicsHow-to TechHow to Unlock a Cell Phone or SmartphoneElectronicsCell PhonesCan extreme weather damage your cell phone?ElectronicsTravel GadgetsHow Wind-up Cell Phone Chargers WorkElectronicsCell PhonesHow to Tether a Cell PhoneElectronicsCell PhonesHow did digital technology change cell phone service?ElectronicsCell PhonesHow to Unlock an Android Cell PhoneElectronicsCell PhonesScientists Have Invented a Battery-free Cell PhoneElectronicsCell PhonesHow to Decide Between a Smart Phone and Cell PhoneElectronicsTelephone TechnologyHow to Forward Calls from a Landline to a Cell PhoneElectronicsCell PhonesHow to Import Pictures from a Cell Phone to a LaptopElectronicsTech's Effects on the Family5 Ways to Keep Your Kids Off Their Cell PhonesElectronicsTech for KidsCell Phones for Kids: When is the right time?ElectronicsCell PhonesWould a cell phone work on a submerged submarine?ElectronicsCell PhonesHow to Transfer Data from One Cell Phone to AnotherElectronicsCell PhonesCan you use a cell phone as a credit card?ElectronicsCell PhonesWhy is a cell phone called a cell phone?ElectronicsCell PhonesElectromagnetic InterferenceElectronicsCell PhonesWhat does GSM mean in a cell phone?ElectronicsCell PhonesHow does a vibrating cell phone or pager work?ElectronicsCell PhonesHow GPS Phones WorkElectronicsHow-to TechHow to Unlock GSM PhonesElectronicsCell PhonesHow Smartphones WorkElectronicsCell PhonesCell-phone CodesElectronicsCell PhonesCell-phone Frequencies - Cell phone FrequenciesElectronicsCell Phone AppsHow to Fake a GPS Location on Your PhoneElectronicsWirelessHow 5G WorksElectronicsTelephone TechnologyWhy does the phone still work when the electricity goes out?ElectronicsCell PhonesHow Cell-phone Radiation WorksElectronicsCell PhonesHow Cell-phone Viruses WorkElectronicsCell PhonesHow Cell-phone Implants WorkElectronicsHigh-Tech Gadgets5 Tips for Picking the Right SmartphoneElectronicsCell PhonesCell-phone Network Technologies: 3G - 3G Cell phonesElectronicsCell PhonesInside a Digital Cell PhoneElectronicsWirelessHow 4G WorksElectronicsCell PhonesDo Smartphones Really Charge Faster in Airplane Mode?ElectronicsCell Phones4 Reasons Your Phone Keeps Dropping CallsElectronicsCell PhonesPotential Health Risks - How Cell-phone Radiation WorksElectronicsCell PhonesSmartphone Hardware and Software - How Smartphones WorkElectronicsCell PhonesCell-phone Channels - Cell phone ChannelsElectronicsCell PhonesSource of Radiation - How Cell-phone Radiation WorksElectronicsCell PhonesCell Phone Jamming DeviceElectronicsCell PhonesAnalog Cell PhonesElectronicsFuture TechWhat Will Replace the Smartphone?ElectronicsWirelessHow WiFi Phones WorkElectronicsTelephone TechnologyDo smartphone covers really protect phones from damage?ElectronicsCell PhonesCell Phone Jamming Legal IssuesElectronicsCell PhonesCell Phone Network Technologies: 2G - 2G Cell phone NetworksElectronicsCell PhonesCell Phone Jamming BasicsElectronicsCell PhonesGSM and CDMA - How Cell Phones WorkElectronicsCell PhonesCould someone stalk you using your own smartphone?ElectronicsCell Phones6 Creative Uses for an Old SmartphoneElectronicsTravel GadgetsIntroduction to Global Cell Phones