1. Flip phones are more compact, which is valued by the Japanese.
2. Unlike English, the traditional keypad is perfect for inputting Japanese text. In fact, touchscreen smartphone Japanese keyboards essentially mimic this setup[0].
Yeah. The Japanese have always been fond of their flip phones, and in fact they were well ahead of us on smartphones. Long before the iPhone and such, they had very powerful flip phones there made by Sharp and such.
Except even with those phones (now called 'garakei'), the software was still awful, and the ecosystem was still locked shut -- getting an app onto the phone took a lot of sweat, and a lot of connections.
Well, not really. Getting an app on a docomo phone for example was extremely easy, as in create the app and put it online. You had to be a verifiable company to touch the encrypted bits (user ID, encrypted NFC etc) or to make payments (which are then carrier handled payments), but that
about all.
The other carriers needed paperwork even for free apps, but not so much more.
About the software, it was barebone compared to iPhone apps, but you could run an app for three days without crashing or dropping a single call. The scrutinity towards quality was equivalent to home appliances' level. The iPhone brought the expectations of reliability close to Windows PCs.
There are 2 reasons for this:
1. Flip phones are more compact, which is valued by the Japanese.
2. Unlike English, the traditional keypad is perfect for inputting Japanese text. In fact, touchscreen smartphone Japanese keyboards essentially mimic this setup[0].
0: http://i.imgur.com/XFTMc.png