Mobile phones get lost all the time. Sensible folk will usually have some kind of access control code in play so that anyone getting hold of a misplaced device will not be able to read their texts or steal their identity.
This also means however that the device is very hard to return to its owner. Even if there is an address or telephone number attached, someone finding a lost phone may be unlikely to bother to make use of these.
These days there are phones which are specially designed to be ultra-robust. Taking that a step further allows for the creation of a phone which can happily withstand being sent through the post with zero packaging.
These phones would each have a combined barcode and numerals etched on the outside surface by the manufacturer.
When a lost phone is simply dropped in a postbox, the barcode allows it to be scanned and sorted by the normal postal equipment, returned to a regional office of the maker and eventually delivered to its owner, without displaying any easily readable personal identifiers.
After return of the device, a reward might be arranged when a returner enters the etched numerals from the device into a web form.