Hello, that's right, you don't need a plan for the Ultrahuman Ring.
For me, the ring is not an alternative, but an additional and useful gadget. It gives me various data, e.g. also on sleep, which fascinates me (without activation as with the Apple Watch).
The only negative point for me is that I have to charge the ring every 72 hours, which is far more often than advertised.
Otherwise, I'm very happy with it and it feels great to wear.

The Ring can be used without a plan. It is not an Apple Watch alternative.
I have returned it!