Well, sorry if I hurted you, this was not what I meant...
It's just that you don't seem to take the time to understand what I say...
I said:
An as an FYI, you can see this number never mind a poor vision in your phone:
Settings → General → About → IMEI...
To what you replied:
That is for the iPhone's IMEI number which is unique to each phone.
If I get a new SIM card, my iPhone's IMEI number does not change.
The phone's IMEI number simply matches the one on the SIM card, and that's the exact reason why this number must be registered with the phone, and that's the exact reason why the IMEI number in your phone won't change if you put another SIM card inside, WITHOUT REGISTERING IT, WITHOUT ACTIVATING IT with iTunes to your carrier's network.
If you get a new SIM card and register it with your carrier, the IMEI number in your phone will reflect the one on the new SIM card;
If you do not register (activate) it, the IMEI number in your phone won't reflect the one on the SIM card, but you won't be able then to make any call, except the 911 one.
Serial Number = Phone's identity.
IMEI = SIM card identity
Both must be paired (activated) for your phone to work.
Make sense ?
☺