[steve19]

I assume this is so they can log cell phone/tablet IMEI numbers and/or MAC addresses at the airport while the foreigners queue to be finger printed and photographed?

If they log the IMEI they can track most foreigners as they move around the country. Even if they are not bringing sim cards, the phones will still try to connect to a local network to allow emergency calls.

Or maybe so they can confiscate and download the contents of electronics devices quickly with as little delay as possible (it can take 5-10+ minutes before a completely dead smartphone has enough charge to complete a boot up).

[pudquick]

Then include your device, powered on in airplane mode, in an easy to reach pocket.

Easy to prove it's on, just don't take it out of airplane mode until you arrive at your destination. In flight you could power it off & back on before touchdown to preserve battery.

[rb2k_]

Actually, in the line that I usually wait for to be finger printed and photographed, there are signs everywhere telling you to NOT use a cellphone.

Seeing as it can take up to an hour, most people would probably love to do so.