Voluntary my ass! I remember not too long ago reading or hearing how the UK and EU governments were requesting handset makers buck up their security because too many phones are getting stolen.
This is their response, they'll sell it as voluntary, but in reality they were most likely told to sort it out or else.
The politicians getting confused. Phones already had unique IMEI's so that stolen phones could be backlisted. Unfortunately the networks weren't, in general, maintaining black lists. The networks were seen as benefiting from phone theft.
That was back when phones were mainly used for making phone calls.