By Nicholas Smith Updated January 22, 2019
After you purchase and use your cellphone for an extended period of time, you can change networks. However, the phone that you’re currently using may not be offered on that network. If you wish to keep using your current handset but use another network, you must unlock your phone. This means that you unlock the phone to accept another subscriber identification module. The SIM card itself isn’t unlocked.
Most cellphones you buy have SIM cards installed in them. SIM cards are memory chips used in cellular devices to store your account’s information, your cellphone number, your phone book, text messages and other data. Because they contain such sensitive information, avoid removing them from the phone unless absolutely necessary.
Unlocking a SIM is often done to change the service carrier or to remove the phone for sale. The new owner will require an unlocked phone to install and use their own SIM card.
Locked SIM Cards
Unless you specifically purchased an unlocked phone, your phone is likely to have a SIM lock on it. This feature prevents you from taking a particular provider’s phone and using it on another network. The lock helps keep devices on their originally assigned networks. However, most devices can be unlocked using a SIM unlock procedure.
You can remove the SIM lock by performing an unlock procedure on the phone. Although the specific unlock instructions differ according to your phone model, the procedure consists of obtaining an unlock code from your existing mobile provider. You can also buy a code online if the provider is unable to give it to you. After you obtain the unlock code, you install another network’s SIM card, power on the cell phone IMEI unlocking service and then enter the unlock code when prompted.
Just because you unlock your phone doesn’t mean that you can use the phone on any network. The SIM card for the new network must compatible with the network your phone currently supports. The major networks – T-Mobile, AT&T, Verizon and Sprint – are either GSM or CDMA networks. Therefore, if your phone is a GSM phone, you can’t use it on the Sprint network, as Sprint operates a CDMA-based network.
International SIM Cards
One common reason for unlocking a phone is to use the device internationally. Most countries have their own SIM cards and you can purchase a SIM and a phone plan in a different country while visiting. In this case, you must unlock the phone and actually remove and replace the old SIM card with the new SIM card to gain compatibility on the country network.
For example, Mexico uses TELCEL service for their entire country. If you unlock your phone, you can replace the SIM with a TELCEL card while visiting and enjoy a data plan with local and even international calling at a much reduced rate. Using this system is common for long term travel where alternating service plans according to location is useful.
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Nicholas Smith has written political articles for SmithonPolitics.com, “The Daily Californian” and other publications since 2004. He is a former commissioner with the city of Berkeley, Calif. He holds a Bachelor of Arts in political science from the University of California-Berkeley and a Juris Doctor from St. John’s University School of Law.