Modern smartphones seem to pack quite a load.
I got a Samsung galaxy note 4, which boasts 3Gb of RAM and 8 cores.
One wonders - what if...?
Well, i compiled my standalone miner for it, and sadly it only does a hash per 138 seconds.
That is a bit too much for real use, since the average block time is 150 seconds.
Core count does not help here (only 3 are usable with this much RAM and OS load), since even if all of them were to make a hash, you'll get 8 hashes that are too late rather than one hash that is too late.
Mine managed to wedge in two hashes over 15 minutes of run time, but only thanks to long inter-block times that won't be common on the real net.
So, with this kind of hash time and block time, latency is everything - you can't just upload the code to every fridge and lightbulb and get a slight improvement by sheer quantity over quality.
You need machines that can do at least one hash every minute.
MIPS laptop, Loongson CPU, 2Gb RAM. Takes 800 seconds to solve, useless.
ARM dev board, 1Gb RAM, Takes 300 seconds to solve, useless.
MacBook 2009, 2Gb RAM, takes 80 seconds to solve, useless.
In the end, i would guess the toppest of the top phones might be usable, but in general you can't mine on devices.
Which is rather sad...
Anyway, that was the "what if" of the day. Back to work.