Samsung Galaxy S21 Ultra: 1 physical SIM + 1 eSIM can be active together at the same time, and up to 5 different eSIM profiles can be stored on the phone in total. So, you could convert the Ultra Mobile SIM to an eSIM (steps below), or you could take your passport and phone to your nearest service center for your Thai mobile carrier and ask them to convert your physical Thai SIM to an eSIM. Just hand them your phone, and they’ll do it for you. If you want to convert the Ultra Mobile physical SIM to an eSIM, install the Ultra Mobile app on your phone and log in: Tap Account on the bottom menu. Tap Order Replacement SIM. Follow the steps to convert and install the physical SIM as an eSIM.