How can iphone xr make both primary and secondary cards receive SMS?

After getting the iPhone XS Max, the author immediately began to test the dual card function. It is found that Apple's dual card dual standby sounds beautiful, but the actual experience is extremely poor, mainly because dual access and dual 4G cannot be realized, that is, two numbers cannot use the telephone function at the same time; Moreover, the dual telecom card can't be used, and the secondary card has no service. Let's take a look at the dual card slot of iPhone XS Max. It is not a traditional double independent card slot, but a single slot and double-sided design, that is, one card is placed on the top and one card is placed on the bottom. The advantage of this design is that it can minimize the occupation of internal space by the card slot.