Sim cards and carriers, discussion

[mini-DIN]

For Japan providers:
SoftBank: doesn't work. They literally can only support iPhone, Android, and garake (which are flip phones, which all run AOSP Android if they support 4G LTE, WiFi, or both).
Rakuten Mobile: works! No IMEI locking, no specific OS only, no other shinanigans. And on top of that they're way cheaper too. Although just like with SoftBank, their ID verification AI can't read my ID, so I had to let SAGAWA (one of the many postal service companies) verify at the front door instead.

Docomo appears to work, too! I haven't tested it extensively since swapping the SIM and adapter in and out is a pain, but Docomo sent me a text with a URL to get the APN info. After configuring that, mobile data worked.

I sent and received texts and received a couple voice calls. Making a call failed, but I've been too busy to test it again.