@dansup I have a disposable SIM I use when I have to give it a phone number, so I'm already in a weird category. That said, I can be persuaded to use that number for registration if I have to.

But I'd honestly be reluctant to trust any site that said this, because:
* if it's genuinely not stored, a spammer can use the same number for 10,000 registrations and then just get another number, or
* some process will complain about the number being reused, showing it *is* being stored somewhere.