> But 3G is being shut down by many operators and more to come. So voice downgrades to 2G, but 2G has a very low limit of concurrent calls, let's say a few dozen. So it's possible that your dumbphone won't work at all.
2G is being shutdown too (IIRC, I had a 2G pay-as-you-go phone that stopped working years ago), and it would be surprising to me that a carrier would shutdown 3G before 2G.