IMEI on GSM in the UK: Do phones broadcast their IMEI to the network?
May 28, 2014 5:54 AM   Subscribe

When GSM phones in the UK are on a 3G network, is there any broadcast or query of the handset's IMEI number to or with the network operator?

This question comes out of a long, long dispute with T-Mobile UK.

I'm curious as to the relationship between IMEIs, SIM cards, and the GSM network. Presumably, the network can issue a packet that prevents blocked handsets 'registering'* with the network, or informing them that they are not welcome.

Is there any communication of IMEI numbers from the device to the network operator, though? Is there a way a network provider can map between a SIM card, a handset, and an account? Are IMEIs provided when devices turn on and associate with a network?

I am likely to be using ambiguous language, due to not being a GSM engineer; clarification happily provided on request!

* I have no idea how this really works
posted by davemee to Technology (5 answers total) 1 user marked this as a favorite

IMEIs can definitely be blocked at the network level, if that's the point of your question. They don't do that in the UK yet - though it's coming, apparently. This might be useful.
posted by DangerIsMyMiddleName at 6:08 AM on May 28, 2014 [1 favorite]

Response by poster: Thanks DangerIsMyMiddleName - it's not so much blocking, which I'm aware of, but advertising. Is a telecom company at all aware of what device is being used with a particular SIM card?

This is still vague in my mind - for an IMEI block to work, for example, does the device identify itself to the network to be told it is blocked or not, or does the network send out a broadcast list of blocked IMEI numbers, which the listening handsets respond to by shutting off their access?

I see references to an IMSI, which is new to me, which seems to be a mechanism to identify a subscriber from the SIM card - but at what point does the IMEI, if at all, come into play?
posted by davemee at 6:30 AM on May 28, 2014

A quick perusal of the UMTS documentation online suggests that the IMEI is not part of the authentication vector but the network can request the IMEI of an attached device if it wants it.

(eg: UMTS Security)
posted by pharm at 7:17 AM on May 28, 2014 [1 favorite]

Best answer: Hi. I've worked for mobile operators on both sides of the Atlantic, although I haven't worked for T-Mob.

TL;DR: The network operator has your IMEI, and maps it to your SIM and your account.

Your IMEI is a unique identifier for your device. You can swap different SIMs into that device, but the IMEI will remain the same.

The telecom company is very much aware of what device is being used with a particular SIM card.
The big driver is lost and stolen handsets, which we deal with with something called an equipment identity register (EIR). When a phone joins a network, and in some of the subsequent signalling between the phone and the network, the IMEI of of the device is checked against a database of handsets that have been reported as lost or stolen, and either allowed or barred accordingly.
Cleverer operators will do things like map the first bit of the IMEI (called the TAC) to a list of known device models and do things like push custom ads to you, or target their upgrade pitches better (e.g. if you're on an iPhone 4S, tell you that the 5C is available for only 100 quid on a 24-month contract, etc.)
posted by Kreiger at 10:16 AM on May 28, 2014 [1 favorite]

Response by poster: Thanks again for everybody's responses - Kreiger, pharm, and DangerIsMyMiddleName. They have been insightful and appreciated. As I understand it, telcos do not query IMEI numbers of active devices with operational SIM cards unless they want to monetise you. Devices present their IMEIs to networks when joining them, which is the basis of IMEI blocks as per the EIR.
posted by davemee at 1:21 PM on May 28, 2014

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