So I recently bought a Samsung 20 FE and its unlocked and doesn’t have a sim card. I’m upgrading from a S6(Huge improvement!). I decided to go with mint mobile and they are sending me a sim card within 1-2 weeks. I’m not really sure how sim cards work but can I use my old sim card and insert it on my new phone as temporarily? or will the phone lock it to my old carrier(straight talk) once I do? Or should I just keep using my old phone just to be on the safe side.