> reflashing every serial number in flash/EEPROM with 0x00.

It will be an amazing video, but good luck if the device in question has (very likely):

* a mask-ROM / OTP-ROM for a serial number - almost all microcontrollers and EEPROMs sold nowadays has at least one permanent and unchangable UUID for hardware tracking and DRM implementation (security-through-obscurity tricks to prevent rogue competitors from copying your firmware).

* "firmware read-protection" - which means the only way to dump the EEPROM is performing a full-chip erase and destroy the entire firmware, commonly used in embedded systems to stop rogue competitors from copying your firmware.

I just knew that RAM DIMMs usually have a 24 or 93 series chip on them, and figured that could be re-programmed (or replaced with a reprogrammable version if the existing chip is non-compliant).

In many cases, a) the unique id's are in read-only parts of the flash and b) the system firmware won't work if it can't read a unique id that matches a (signed) stored ID somewhere in its system.

In many cases, this isn't for anything user-facing. Unique ID chips can be very useful for detecting factory-overrun counterfeits ("oh, your $widget does this notable, nonfunctional behavior? Where did you purchase it, perchance?").

> It’s not like any of these are phoning home (I hope)

Firmware is largely closed-source, so all you can do is hope.

Changing the IMEI number of a phone is illegal in many countries.

My phone required it.

When purchased, it had an IMEI of all zeroes, and came with a step by step guide to setting the IMEI from my old phone into it.

Apparently that works around phone providers who blacklist or whitelist certain manufacturers.

Can you please expand on your phone? What model is it? It sounds very unusual for the user to be able to change the imei.

A knock-off Umidigi A3 Pro.

It's an awesome Chinese $50 android phone.

Because it hasn't passed all the network tests, most mobile networks would block an entirely random IMEI, so they suggest you type in the IMEI from your old phone (as long as it's 4g - if it isn't, they have a support email address you can contact and they'll give you an IMEI that works in your country)

Even the legit Umidigi A3 Pro's (which cost $80, and have proper certifications) have an 'imei change' tool.

Not for long I'll wager...

I'll wager the opposite. Of course it's not legal anywhere, but I don't expect any customs people to be able to tell that a phone comes with an changeable/unapproved IMEI.