android device id confusion

Question

If I dial * # * # 8 2 5 5 # * # * ,

Answer 1

IMEI

There is a mandatory requirement by the standardization bodies, that mobile devices for public networks may be uniquely identified by the IMEI number

It is the manufacturer's responsibility to set IMEI. In practice, developers sometimes see IMEIs like 000000... or 123456... Sometimes phones with identical IMEI go to production, which of course is a bug that should be fixed...

ANDROID_ID

A 64-bit number (as a hex string) that is randomly generated on the device's first boot and should remain constant for the lifetime of the device. (The value may change if a factory reset is performed on the device.)

It looks like Android does not trust the manufacturers and provides an alternative unique ID.

EDIT:

This is what I get (instead of IMEI) on and Android device that is not a phone:

$ adb shell dumpsys iphonesubinfo
Phone Subscriber Info:
  Phone Type = GSM
  Device ID = null