On the mobile phone, is there a "mac address" that makes each mobile phone different?

Question

In other words, is there an ID for each and every mobile phone--that makes it different.

No two phones can have the same ID. (I'm talking about smartphones ...android, iphone, etc)

Answer 1

Phones have MAC addresses on WiFi interfaces, but the cellular interface has something called an IMEI, that performs roughly the same function.

Answer 2

It's worth noting that the IMEI is linked to the physical device/phone, as opposed to the IMSI which is linked to the SIM card and therefore the customer account. Not sure how you'd go about getting hold of either from within an app running on the phone, assuming that's what you're doing.