dasaint100 Has there been proof of certain apps broadcasting the phone IMEI?
I have seen advice for people in countries where IMEI changing is legal that they only change when the sim is changed as the sim would be an identifier anyway.
With airplane mode on, do WiFi routers take in the IMEI of the phone and broadcast it?
Apps have no access to these identifiers, with exception of the currently enabled carrier-based messaging app for SMS/MMS/RCS which is a special case that's given access to certain device identifiers including the IMEI. You would have to install a messaging app for this and configure it to be your default app for this to happen.
IMEI does not change when the SIM is changed, it is an identifier of the device, not the user / SIM, you are likely confusing this with IMSI. These two are also not the only identifiers / data points to identify a user over the cellular network: https://grapheneos.social/@GrapheneOS/113319956422621755
IMEI has nothing to do with WiFi. They aren't broadcast to WiFi networks.