This is terrible news. I wanted to get a sim card for Japan, but you can only get a pocket wifi device, which isn't so bad, but not as straightforward as swapping your sim out for a local sim as i do when in the states or malaysia.
That's not true. You just can't get a sim card with voice/SMS capability.
Foreigners can get data only SIMs no problem, most airports will sell them (often out of a vending machine)
e.g. https://t.iijmio.jp/en/
Given VOIP, what is the rationale of making this distinction?
So voice SIMs can't be used as throwaway cell numbers, I'd guess.