How to unlock a phone locked to Verizon, AT&T, Sprint, or T-Mobile

If you bought your phone from a carrier's store, then it is most likely locked. Same goes for carrier-branded phones sold via retailers and online stores. Still, there's a relatively easy way of checking whether or not that's the case. Simply swap your SIM card with one from another carrier – you can probably borrow one from a friend or relative. If the phone works fine with your buddy's SIM card, then great success! That means your phone isn't locked. If it doesn't, then read on to learn how to unlock your handset. 

The conditions you have to meet in order to have your phone unlocked for free may differ slightly from one carrier to another. Yet in general, it boils down to the following:

AT&T has a web page dedicated to cell phone unlocking right here, along with an online request form. In a nutshell, your device has to be active under your account, and if you took advantage of an early upgrade, you must first wait for your 14-day return period to expire before requesting your unlock code. Postpaid customers must have been active for no less than 60 days before unlocking. Prepaid customers must have been active for at least six months of paid service. Keep in mind that it might take up to 2 working days before you receive your unlock code. When filling out the unlock request form, you'll need to provide the device's IMEI number. Here's how to find the IMEI of your handset.

The good news is that the majority of Verizon phones, although designed to be used with the carrier's CDMA network, come with an unlocked GSM SIM card slot as well. This applies to 4G LTE devices and most 3G devices activated on the carrier's postpaid service. Only Verizon's Global Ready 3G cell phones might ask you for a code when switching to another provider's service – just type "000000" or "123456" and you should be good to go. The bad news is that network compatibility and coverage might be an issue, depending on your device's specifications and on the frequencies the carrier you're switching to provides service on. It is best to contact your carrier before bringing a Verizon phone onto its network.

For more details, read Verizon's device unlocking policy.

Let's say that your phone was launched before February of 2015 and is technically capable of being unlocked. In that case, Sprint will let you know that you're eligible for an unlock either via text message or in your bill notification. You'll have to contact Sprint Customer Care for assistance at that point. Phones launched after February 2015 will be unlocked automatically when eligible. It is also possible to unlock inactive devices, although the process may require over-the-air updates to be performed. Contact Customer Care for specific instructions. Keep in mind that even if you have your Sprint phone unlocked, it may not be fully compatible with other carriers' networks. Best results should be expected when moving to a Sprint MVNO, such as Boost Mobile, Virgin Mobile, FreedomPop, or Ting. Regardless of which carrier you're switching to, contact them to ensure that your unlocked Sprint device will work on their network.

For more details, read Sprint's device unlocking policy.

You must contact T-Mobile's Support Service to request an unlock code for your phone. To be eligible, a device must have been active for no less than 40 days on the requesting account. As far as prepaid phones go, they must have been active for at least a year. Furhermore, smartphones must have been refilled for at least $100 before they become eligible. The requirement is only $25 if you have a basic phone. We must also mention that a line of service is allowed no more than 2 unlock codes per 12 months of service.