I'm tentatively going to say add me to the list of those for whom a replacement sim card did the trick. Made about 8 calls since, long and short, no problems yet. As a couple people have mentioned, the contacts on my replacement card look different than my original one - photo attached. The card on the right with the oval center pattern is my replacement, which I got from a different store than the one I bought the phone from.
Everybody still having problems have a card that looks like the one on the left?
Edit: I'm still having the issue with the new (oval) card, as is at least one other user. Ah well,.