[dotancohen]

I'm basing the definition on the usage of words by the companies which manufacture and market the devices. See the usage of the words "phone" and "smartphone" on the LG, Samsung, and Xiaomi websites.

Apparently, the "phone" in "smartphone" is about as relevant as is the "fun" in "funeral".

[Izkata]

The evolution of the meaning is even more obvious in at least one other language: Japanese borrows the English word "smartphone" for those, but uses "denwa" (with its own kanji) for non-smartphones.

[quietbritishjim]

Sure, I agree with that. (But also, what marketer would miss an easy opportunity to include "smart" in their product's description.) I was just talking about your last paragraph.