IMEI numbers (from *#06#)

[M4cruiser]

I have an odd question about IMEI numbers.
I have had several phones over the years and the IMEI has always started with a "3" - except just one mobile handset on which the number starts with a "4", and it's by no means the newest one, so they aren't issued in sequence.
Does anyone know why this is, or have any information?

[camel_landy]

There's a little Wiki on it here:

https://en.wikipedia.org/wiki/International_Mobile...

In short, the IMEI is made up from a number of blocks. The prefix is allocated by BABT (British Approvals Board for Telecoms), who are the IMEI allocating authority.

HTH

M

[alorotom]

Lots of new phones have multiple IMEIs as well.

My iPhone 11 - the first begins with a 3 and the second with a 4 - it was purchased in the US if that makes any difference.

[weeboot]

alorotom said:

Lots of new phones have multiple IMEIs as well.

My iPhone 11 - the first begins with a 3 and the second with a 4 - it was purchased in the US if that makes any difference.

UK sourced 12 Pro has two 3s...
After a bit of research it turns out that the first two digits of the IMEI code is the organisation that entered the information into the registry. The manufacturer of the mobile device can contact any organisation.

Code	Registrar Organization IMEI	Origin
00	Test IMEI Nations with 2-digit CCs
01	PTCRB	United States
02 – 09	Test IMEI Nations with 3-digit CCs
10	DECT devices ?
30	Iridium	United States (satellite phones)
33	DGPT	France
35	Comreg	Ireland
44	BABT	United Kingdom
45	NTA	Denmark
49	BZT / BAPT	Germany
50	BZT ETS	Germany
51	Cetecom ICT	Germany
52	Cetecom	Germany
53	TÜV	Germany
54	Phoenix Test Lab	Germany
86	TAF	China
91	MSAI	India
98	BABT	United Kingdom
99	GHA	For multi RAT 3GPP2/3GPP

[anonymous-user]

My business supply expert witnesses and forensic analysis of tech and telecoms data to courts. I could talk about IMEIs for hours!

An IMEI is 15 or 16 digits long (14 or 15 specific numbers with a check digit at the end) and can be broken down into Four parts with a check digit. TAC, FAC, SNR, SVN and check digit.

The first 6 digits is the TAC or Type Allocation Code. This code can be broken down further and includes the manufacturer and handset or device.

The next set of numbers is the FAC or Final Assembly Code. This identifies the final production stage and can include software info. It consists of 2 digits.

The next set is 6 digits long and called the Sequence Number. Its an individual sequence number that uniquely identifies each device, including the same TAC and FAC, and is 6 digits long

The next set of number(s) is the Software Number. It identifies the software version of the device.

The last number of the IMEI is always the check digit. It uses the Luhn algorithm to add a number to the end of the IMEI to check the number is correct. It's not a particularly complex calculation but it is very clever. It's also used on other things with large numbers such as credit cards. It simply allows the system to check the number being given, such as the IMEI to the network or the credit card number to the operator, is correct without it needing to send all data and wait for the response. It can do the calculation locally to confirm it's a viable number before then sending it onward.


https://en.wikipedia.org/wiki/Luhn_algorithm

[M4cruiser]

Interesting information, thank you all.
My phones that have dual SIM have two IMEIs, so I guess it's one per SIM.

I thought a check digit might be involved, but I didn't know all the other blocks. ...

[arcturus]

sebdangerfield said:

The next set of number(s) is the Software Number. It identifies the software version of the device.

Can you clarify this one for me. Software versions are regularly updated during the life of a phone but I assume the IMEI doesn't change with each software upgrade? Or does it just denote the software version it was shipped with?

[anonymous-user]

M4cruiser said:

Interesting information, thank you all.
My phones that have dual SIM have two IMEIs, so I guess it's one per SIM.

I thought a check digit might be involved, but I didn't know all the other blocks. ...

That's right, everything that can access the mobile network must do it via an IMEI of its own so if your phone is dual SIM then it'll have dual IMEI. Some phones utilise dual SIM (or Tri SIM) technology differently by either using a separate transceiver for each SIM or using one. Because of that the IMEIs of a dual SIM Samsung compared to a dual SIM Nokia will have the consecutive number in the IMEI in a different place.

[anonymous-user]

arcturus said:

Can you clarify this one for me. Software versions are regularly updated during the life of a phone but I assume the IMEI doesn't change with each software upgrade? Or does it just denote the software version it was shipped with?

You're right, it seems strange to mark the software version on a phone at point of sale when we think of the frequency of OS updates but when this was brought in in the early 2000s it was realised the IOT was imminent and cars were appearing with embedded SIMS. All these new devices capable of connecting to the mobile network needed an IMEI in order to do so and at the time of developing IMEIs nobody foresaw vacuum cleaners, cars or watches needing IMEIs so work was done to increase the number of available IMEIs.

It was decided to increase the TAC (type allocation code) at the start of the IMEI from 6 to 8 digits as a neat solution to increase the number of IMEIs available massively and at the same time have a way of telling the networks the carrier settings of the device. In terms of your phone it's the settings it was shipped with which can still be important years later even after OS updates but it's hugely important for the SIMs and IMEIs embedded into vehicles and IOT devices which don't necessarily have the computing power of a smart phone backing them up to keep them connected to the network.