It happened: you took advantage of holiday season sales to buy yourself a new smartphone. Now it’s time to sell your old one or hand it down to a relative, but they use a different carrier. How do you make that happen? In some cases, you don’t have to do anything at all.

After the mobile phone industry agreed to voluntary unlocking standards in 2013 that finally took effect in 2015, unlocking your phone should theoretically be easier than it used to be.

Across all carriers, there are some things that can cause problems along the way. If you’ve had a warranty replacement from the manufacturer, for example, the carrier and manufacturer may not agree about whose job it is to unlock the device. Multiple readers, for example, report having their request kicked back and forth between AT&T and Apple.

A secondhand phone that you buy may also have been reported lost or stolen, or “involved with fraudulent activity,” making it ineligible to be unlocked. Even a new phone that you buy secondhand may not meet the requirements for unlocking: especially for phones purchased before 2015, never assume that paying full retail means that your device will be unlocked.

When buying a phone secondhand or using a hand-me-down, ask the original purchaser to unlock it before handing it over, preferably showing you the e-mail or other notification from the original carrier.

In addition to information about the original owner, you’ll also need your IMEI, the identification number for all mobile devices: how you find that will vary by phone model.

(Note: We are aware that services of questionable legality exist where you can buy an unlock code. These are not necessarily condoned by your carrier or phone manufacturer, and they aren’t free, so we aren’t going to tell you how to do that.)

AT&T

To kick off the process, go to the carrier’s Device Unlock page, where you’ll be asked for your information, some information about the original owner of the phone if it isn’t you, and of course the IMEI. Your account must have been activated for at least 60 days, and have no past due balance.

Sprint

Your phone needs to be paid in full, and have been activated on the Sprint network for at least 50 days. Prepaid Sprint devices are not eligible for unlocking.

Sprint claims that devices that can be unlocked for use on a different carrier are automatically when the contract is over or the phone’s installment plan has been paid off.

That’s generally any smartphone produced since carriers agreed to voluntary unlocking standards that went into effect in early 2015: when a phone compatible with other domestic networks is eligible, you can take it to any carrier you like, as long as it’s compatible with their network.

T-Mobile

T-Mobile goes with self-service, at least for Android users: if you only have one device to unlock and it’s an Android device, you can use an app. Everyone else has to contact the un-carrier over the phone or using another method of communication. The phone must have been activated for at least 40 days.

Verizon

This one’s easy: newer Verizon devices are sold without a lock that would prevent you from taking it to another carrier, though you still have to complete the terms of your installment plan or contract. Some prepaid phones are locked, and you can call (888) 294-6804 after 12 months to obtain the unlock code.

Your Stories

All consumer transactions can go wrong, and phone unlocking certainly isn’t an exception. Have you had a frustrating experience with getting your phone unlocked, especially after the CTIA standards went into effect in the spring of 2015? We want to hear about it. Write to tips@consumerist.com with “Unlocking” in the subject line.

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