S6 920FD (duos) default sim for group

Hey, I have S6 duos. And I'm wondering if it is possible to set default calling sim for each number of contact group. Eg. I have group called "Colleagues" and I want to call them always using 1-st or 2-sd SIM.

Thanks.

My Galaxy S6 Dual Sim (920FD) isn't getting LTE on AT&T

I have properly signed up for the wireless service on AT&T and I'm seeing 4G, H, or H+ on top of my device instead of LTE. I checked with AT&T and they said that my plan shows that I should be on LTE. I'm in Chicago downtown, so the coverage is not an issue..

I've also checked the LTE frequency and it does consist of band (2,4,5,17). What could be the issue?

Difference in Galaxy S6 Duos 920FD and 9200?

I'm going to be using it with AT&T(US) and SK Telecomm(Korea)

I want to know what the differences are. Also, what is TD LTE? Does this matter in US or S. Korea?