More progress on the road towards a better travel smartphone set up: learned how to open the SIM card slots on both my old & new smartphones (asked the internet how). Then, phoned my cell phone service company & requested my (older) cell phone to be unlocked; “done” right then over the phone. If not sure, might be fairly easy to find out if yours is locked. I did read online that for the last several years many of the phones my carrier sells are unlocked, but I still wasn’t sure about my own old phone. So I phoned my phone service provider & with the tech’s help we confirmed: my older phone was locked. Requested the unlocking. Unlocking is not always granted; can discuss with your phone service company (and/or check online).
Since both phones are unlocked now, switching should be simple. Staff person @ a cell phone kiosk that sells SIM cards said can transfer the SIM card from older unlocked phone to the other for me, so I will go see them again soon.And I would like to try an eSIM account. But my new Android phone does not have an embedded eSIM chip. One innovative company though, has created physical SIM cards with eSIM capability embedded. Will likely buy one of these eSIM-chip SIM cards from them, insert it in new phone & follow their advice to configure it to my new phone (using an app). Then could start an online eSIM account to purchase & download services for travel to most (all?) destinations. (Sent this company an online question to double check on ordering the correct model of their SIM card for my specific phone; am awaiting reply.)