Of course, if you give them the IMEI it facilitates them listening to your phone calls and tracking your location. The 'checking for stolen phones' thing seems totally implausible to me.

It's quite effective, tbh. Stealing phones is still a way to net loads of money if you know a buyer who doesn't give a damn about the source. Hard-reset the phone so it appears clean and off you go.

The only vendor that actively prevents the usage of stolen phones is Apple, because the owner can remote-lock it even if the phone gets wiped via iCloud.

The ideal way would be if network operators cooperated by maintaining a list of "supposedly stolen" IMEI codes and alerted police if a matching phone tries to log in into the network.

None of the carriers cooperate across borders! The phones that can't just be flashed with a new IMEI are rebirthed overseas.

I'm intrigued that you think that requires an IMEI.

It doesn't require it, but it helps. The IMEI gives away information like manufacturer, device model and rev, and persists across changes in SIM.

IMEI is sent when you register to operator's network, so you get that kind of information anyway. Asking for IMEI at the border links person to a physical device so you have a complete set for tracking.

The point is that the problem "Listen to Ms Jane Robert's phone calls" goes from "Of all phones on the network, identify Ms Jane Robert's" to "Ms Jane Roberts has a phone with IMEI xxxx, log all traffic for all SIM identities; prepare implant for LG G5 sold with Vodafone config."