So I finally got a new cellphone over the weekend, and so far there's been some good news and bad news. . . .
The good news is, despite the SIM card not being entirely compatible with my new phone (which is 5G, and my SIM card SIM 3G), I was able to transfer most (not all) of my contacts and such over to my new phone - I still had to manually re-add some contacts to my list, however.
The bad news is since my old phone had stopped working altogether about a couple of weeks ago or so, apparently my number and service has been suspended, so I'll have to get in touch with AT&T tomorrow to get that straightened out since I don't want to lose my number, nor the plan they grandfathered me into.