Look guys, this isn't that tough.
You're confusing "desirable" and "popular". Popular is a measure of units sold. The (in your words) "crappy calling phone" IS popular. That's not saying that "crappy calling" is in any way desirable. But it IS popular.
Just the same with the 3.5" screen. It IS popular. Whether or not it's desirable is up for debate. But it is popular.
This isn't a case where correlation / causation is applicable. It's a bit of an instance of "a little knowledge is a dangerous thing".
popular |ˈpäpyələr|
adjective
1 liked, admired, or enjoyed by many people or by a particular person or group : she was one of the most popular girls in the school | these cheeses are very popular in Europe.
2 [ attrib. ] (of cultural activities or products) intended for or suited to the taste, understanding, or means of the general public rather than specialists or intellectuals : the popular press.
• (of a belief or attitude) held by the majority of the general public : many adult cats, contrary to popular opinion, dislike milk.
3 [ attrib. ] (of political activity) of or carried on by the people as a whole rather than restricted to politicians or political parties : a popular revolt against colonial rule.
popular
adjective
1 the most popular restaurant in town: well-liked, favored, sought-after, in demand, desired, wanted; commercial, marketable, fashionable, trendy, in vogue, all the rage, hot; informal in, cool, big.
[...]
And yes, the "crappy calling phone" is popular, so is the "3.5" screen phone" - but not necessarily because it makes for "crappy calls", or because it has a "3.5" screen".
p.s.
a) if you wish to imply that your use of the word popular was only to address the fact that the screen is indeed in wide-spread use, then your whole statement becomes tautologic.
b) are ****** remotes and incomprehensible product manuals popular too, in your view? if not, what is the difference?
Addendum:
And, of course the screen size is in fact popular. It is not necessarily, however, the most popular one, just because the top 2 selling devices sports one though. That is what have been argued by me, and others. When asked about their prefence, it could very well be that the _popular response_ would be something bigger, or smaller for that matter.