Tong Family

Like used to be pretty simple. There is a number on a SIM card and you read it out and you got service. Now even when activating a watch they need the IMEI and the EID. Ok, I give up when I look at General/about there an entire sea of numbers and I know it can support up to 8 esims so how does this all work?

EID and SEID are burned into every phone

The first thing is that for every phone, there are two codes that correspond to something that is put in at manufacturing time and never changes, they are:

1. EID. The Embedded Identity Document is used to identify the SIM controller on your device. So there is only one per phone.
2. SEID. Secure Element Identification. This is for the NFC chip in your phone so it can track payments and this is surfaced in the General > About > Cellular list

That means when you get a replacement phone (oops!), even if you shove a new sim into it, it won’t necessarily work, because carriers also will check to make sure the actual phone, eg the EID is correct.

When your phone supports more than one line: IMEI and IMEI2

While the EID is for the SIM Controller (there is only one per phone), the IMEI is more about the connection to the network. Until about five years ago, a phone would only have one of these, but starting with the iPhone 11 or so, you could have an active SIM and an active eSIM, so there are now two numbers you need:

1. IMEI. International mobile equipment identifier. This is the unique number for your phone. It’s like the serial number for the network connection of your phone. For a long time, a phone could only have one active line, so there was one IMEI for every phone but then…DSFA arrived
2. IMEI2. Modern iPhones are Dual SIM Full Active (DSFA) which means you can have two active SIMs. This is super convenient for travel and you can tell the phone to use say data on one line and messages on another for every contact you have. But this means there is another IMEI number for the other line. This is a 15-digit number.

For each SIM or eSIM, you have an ICCID or MEID

OK, we are nearly there, now you have a code for the SIM card, you can think of the as the license a carrier gives you to use their network. Confusingly, there are two different standards for this, original GSM carriers had ICCID, and CDMA carriers had MEID, but these days, given either, a carrier can figure out what your plan is.

1. ICCID or Integrated Circuit Card Identification. This is the number that used to be found on every SIM physical card. It is a 20-digit number. The EID is the virtual version of that with 32 digits.
2. MEID or Mobile Equipment Identifier. This is the same as the IMEI for CDMA 2000 carriers (they have different standards which is where there are both. So all phones have both sets of IMEI and MEIDs but typically you only need one or the other. My iPhone 14 Pro only shows the ICCID for that reason.