Lafiel said:

Btw I've yet to see a phone with cams at both ends of the display.

Do you really need both ends, though? One could be enough to reasonably predict the focus of the other as well - at least enough for the general area for foveation, even if it may not be precise enough for something like aiming. Obviously bespoke hardware would be better, but it could be enough for the entry level.

https://www.youtube.com/watch?v=nUJ77weGvng