During Hong Kong business tripCauseway Bay's Apple StoreI went to. The aim is to know the only iPhone XS Max Hong Kong version that you can "Insert two Physical SIMMs". Stock status is iPhone XS and XS Max, and even iPhone XR which has been on sale further, each color is ample and you can choose anything you want. I bought XS Max 512 GB of the same model that I use in the country immediately. On the spot, confirmation with a light explanation from the store staff "I can not use it in Japan, is it OK?" This is a convenience explanation that part of the corresponding band is different and it is a terminal not yet acquired technical skill. It is easy to tell that it can be used without problems and the purpose of use is double operation of Japanese SIM and local SIM at the destination.

I quickly replicated from the backup, and for the first time in the shim tray I set two hands of au and softbank sims back to back, set. There is a spring on the back side of the shim tray, so the SIM on the back has been devised and it seems to be Apple.

In the mobile data communication setup, each carrier of two SIMs appears properly like this. Separate the voice line to Softbank and data communication to au.

Like this one grabs two carriers in one unit. When I tried over each number in the test call, I received it properly. It is also possible to choose which line to dial on call.
At the travel destination, Japan's SIM is set only for incoming voice calls, and mobile data communication is set as the local tourist SIM. With this, you can do mobile data communication cheaply without missing calls from domestic. If domestic carriers are realized as eSIM, the same usage can be done in the domestic version, is this an ideal system for a while?
By the way, recently, I have acquired Skype number and set it as a Skype application, and I am testing to shift the phone number which does not depend on carrier. There is still no problem such as not being notified of the number at the time of calling, but in the near future I think that the telephone number can be separated from the carrier and the SIM can be selected only by data communication. Ideal if it is possible to make and receive calls with one telephone number regardless of landline phone or domestic or foreign phone numbers.