Few things that come to mind right away but I’ll give it more thoughts.

- People have had issues with bandwidth utilisation when using nostr clients. If I can tie my phone number with my #nostr identify with some kind of two factor handshake memorized on your gateway, then I can text your gateway and it will publish as me on #nostr without having a nostr client running on my phone.

- Client-side setting to relay DM and mentions to my phone via SMS. Which means your SMS gateway would also have to act as a #nostr client on my behalf. Related to the problem mentionned above (bandwidth).

- I could contact someone who’s not on #nostr from my #nostr client (kinda like the blue vs. green message bubbles on iPhones)

- Decentralized autonomous car sharing marketplace. Install a device in your car that can unlock the doors over the cellular network. Client rents the car with LN paiement using nostr client, it unlocks the door of the owner’s car, take the key in the glove box and go. That’s a stretch (admin shit: insurance, paiement guarantee etc) but… one can always dream right?

- I’ll keep thinking of as-useful but less complicated use-case also 😅