SIM cards may not be shared between two devices. Each SIM card is assigned to a device and paired together. You will need to buy a new SIM card.
I CAN'T BELIEVE THAT BOOST IS TELLING ME THAT I CAN'T TRADE MY NOTE 8 (I GOT CASH FROM BEST BUY A YEAR AGO UNLOCKED) BCS THEY LOCKED MY PHONE WITH THEM AND IN ORDER TO TRADE MY PHONE TO GET S10+ I HAVE TO KEEP MY NOTE 8 FOR A YEAR WITH THEM. AND THEN THEY WILL REALISE MY NOTE 8 THAT I PAY CASH AT BEST BUY. So that means that now your new s10 is locked with boost and if tou would like to trade phone in 4 month you cant.