Samsung listened and put a microSD slot back into their flagships with the Galaxy S7 and S7 Edge, which doubled as a second SIM slot. With the phone's storage capped at 32 GB, using the microSD slot was basically a necessity for most users. The issue with that, however, is that using a microSD card only allows you to use one Nano-SIM card. For users who want to have some extra storage and an extra line at the same time, however, there is hope as there is a rather dangerous mod that takes some patience and skill, but, if done right, will result in being able to use a microSD and second Nano-SIM at the same time.
Before beginning the mod, it should be noted that you'll be merging one of your Nano-SIM cards to your microSD card, so it should be your main or full-time SIM. It should also be noted that it is terrifyingly easy to slip up while performing this mod; it does involve a lighter, after all. In any case, the basic gist of it is that you'll be removing the chip from inside your Nano-SIM card and affixing it to your microSD card. The way you'll be removing the Nano-SIM's chip is by heating up the Nano-SIM until the chip's adhesive comes loose, then cutting into the card to retrieve the chip.
From there, you'll have to trim the chip very carefully, align it just as carefully on the bottom of the microSD card and use a bit of super glue or double sided tape. Take note that if you use the super glue, you'll have to be careful to not let any run onto the microSD card's contacts and you won't be able to use the card in any other devices. The double-sided tape is the better option if you'd like to uncouple the Nano-SIM from the microSD at some point, though the bond won't be as strong as that provided by super glue. The mod should look like the last image shown below if you've done it right. Upon inserting the modded card into your Galaxy S7 or S7 Edge, you should be able to manage your storage and both SIM cards as normal.