system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do they keep buying new burner phones on tv shows?

I was watching Burn Notice (amongst other similar shows)  and they go through dozens of cheap phones just binning them after they're done... Why not keep the handset and just use a new sim card which would have a different number etc? Sure the hand sets are individually cheap but if you had to keep buying them it'll add up...
gpt
The SIM card, which has its own unique serial #, stores your phone # and a bunch of other stuff that is unique to your carrier and/or you as a unique subscriber.

The cell phone however has its _own_ unique serial # (several in fact) the most important which is the IMEI number. Think of this as a globally unique serial # for the cell phone.

Police and intelligence agencies that can track and trace cell phones can latch onto a phone's IMEI just as easily as the SIM card data.
In order to trace and track your IMEI, you need to make either a long enough call, or several calls before they can nail you down.

While it may be possible to spoof or change an IMEI #, Im pretty sure they're burned into silicon similar to a MAC address for ethernet devices.