iPhone 6 Plus generally fits in to US size 38 or larger jeans. However the word "fits" here begs a fine print. Once you put that in pocket, you can't put anything else. Also it really "sticks" out and whenever you sit or stand up, you will fill its presence. Even if you solved pocket issue somehow, the fact is that human hands are not made for this kind of size. You really can't type with one hand. On a long phone calls, it's pain to hold on.
The big screen craze is mainly because of people who want to have one device and avoid buying tablets. They are willing to take on pain in exchange of savings for extra money on tablet. However people who can afford having both, iPhone 6 is really the max size where "world in your pocket" ends and "requires a purse or carry bag" starts.
38 or larger? That sounds huge. I don't have any numbers to quote but my guess is that the average for adult men here in scandinavia would be 34. I guess I have to gain some weight so that I can buy new pants for my phone, if it just barely fits in 38 maybe 42 is a good size to aim for.
The big screen craze is mainly because of people who want to have one device and avoid buying tablets. They are willing to take on pain in exchange of savings for extra money on tablet. However people who can afford having both, iPhone 6 is really the max size where "world in your pocket" ends and "requires a purse or carry bag" starts.