To check an IMEI, dial *#06# on the phone and it appears on screen. With that number, the official lookup at portal.crt.gob.mx/consultar-imei tells you whether the device is reported stolen or lost in the GSMA's global database. It has two limits. You get two lookups per user per day, and it only works from a connection in Mexico. A blacklisted IMEI does not work on any network that takes part in that database, in Mexico or abroad.
There are four places to find it, and on a genuine device all four say the same thing.
If you are buying remotely, ask for the IMEI in writing before you pay. A seller who will not give it does not deserve your money. With the number in hand, run the CRT lookup before the device leaves their warehouse.
The IMEI from *#06#, the one in the settings, the one on the box and the one on the invoice all have to be the same. If the box shows a different one, the box is not from that device, and the same goes for the model number. If the invoice shows a different one, the shop's warranty is tied to a device that is not yours. Both are grounds to ask for an exchange or a return within the five business days the law gives you on distance purchases, as explained in your rights when buying refurbished.
A dual-SIM device has two IMEIs. Look up both.
The Comisión Reguladora de Telecomunicaciones (CRT, Mexico's telecoms regulator), which replaced the IFT, runs the official lookup at portal.crt.gob.mx/consultar-imei. It compares the IMEI against the GSMA's global database of stolen and lost devices, which more than 150 operators feed daily, including 38 from 15 Latin American countries.
What to know before you use it:
If the device shows a report, do not buy it, and if you already paid, demand a refund. A reported IMEI stays blocked on the networks that take part in the GSMA database, and there is no confirmed way to reverse that report other than through whoever filed it.
A blacklisted IMEI belongs to a device that its owner or its carrier reported stolen or lost. Networks that take part in the GSMA database reject that device, in Mexico and abroad. In practice, the device cannot register on any mobile network that participates in that database. That is why some people sell them "for parts" at very low prices, and sometimes present them as working phones.
On iPhone it gets worse. A stolen device usually also ends up with Activation Lock, tied to the owner's iCloud, and cannot be reactivated without their Apple ID. There is a documented pattern in Mexico of iPhone theft followed by extortion of the owner for their iCloud credentials, precisely because without them the device is worth almost nothing. Never accept "I will send you the unlock once you pay." More warning signs are in how to tell if an iPhone is original or fake.
A clean IMEI at the CRT is necessary, but not enough. There are four things it does not cover.
How to run these with the device in your hand is in what to check when it arrives.
If you buy a device locked to a carrier, the IMEI is what they will ask you for. AT&T México unlocks for free when the device is fully paid off with no balance owed, through a request to customer service using the IMEI, and usually resolves it in under 24 hours. A device reported stolen or lost cannot be unlocked. The details for each carrier are in US, Chinese or European iPhone.
The limits of the CRT lookup were taken from the description on its own page; reread it before each lookup because they can change.
