And way behind in others. Sims are way over priced. 1Gig is $30 vs say Singapore 7Gig for $20 or Turkey, 15Gig for $15

As another example even though > 40% of users don't have a landline more often than not you can not call a Japanese toll free number (0120) from a cellphone.

There's also the issue that unlike the USA where you can't tell from the phone number if it's a cellphone or a landline, in Japan you can. Cellphone numbers start with 070, 080, or 090 where as landlines start with different prefixes. Because of this you're judged based on your number. A person or company without a landline is judged to be less trust worthy than one with. Oh, and landlines require $700 to start (though that may have been finally fixed)

...and way behind in others. Try finding a pre-paid voice & data SIM in Japan (hint: it doesn't exist due to arcane regulations - non-residents can only get data-only SIMs). Most WiFi spots require registration that require you to confirm identity via a verification email (think chicken and egg).

I hope not to drag this conversation too much down the rabbit hole, but do you have any advise about what and where to get when it comes to a data SIM, which works on a GSM phone in Japan? Validity: ca. 1 month.

I used a pocket wifi from Sakura Mobile when I was Japan - https://www.sakuramobile.jp/

They delivered it to my hotel and it was easy to set things up.

Basically the same (except I used Rentaphone, as mentioned above).