I know nothing of a SIM card, as I have yet to upgrade my phone. Maybe when I get my stimulus check, I’ll treat myself to a camera phone...:o])
Have you rested up?
I'm not sure but I think in the U.S. only T-Mobile uses SIM cards. It's a tiny memory card that has a unique code that the carrier ties to your mobile number. Put the card in a different phone and that phone becomes "yours."
Because my account has Internet access and LoM's doesn't, we sometimes put my card in her phone to download software onto her phone from the Internet (www.getjar.com).
One can purchase SIM cards for international travel or for other countries. (For me it *might* make sense to have a German SIM card, since I am over there so often.)
SIM cards can also hold your phonebook, so that that moves to the new phone along with the card. The downside, as I have learned once again, is that if the phonebook isn't backed up (as mine wasn't -- I hadn't quite yet installed the backup software!) you lose it when the SIM card fails. Mine seem to fail every 5 years or so.
Rested up? No. But I'll make it.
Are you better today?