A MVNO not on T-Mobile that used Passkeys for 2FA and the only way to legitimately port a SIM off the service requires a scheduled in-person interview would be a solid business.

No marketing, all word of mouth from VIPs.

Does that actually work? Like if you're an MVNO aren't you basically just reselling the product of the actual network operator so they can still rug your users?

Made https://reality.eth.link. 

Live in Mashiko, Japan. Mainly skeet about goats.

Also on bsky: https://bsky.app/profile/goat.navy

There's a network layer called SS7. I know of a few people who have illegitimately gotten direct access to it in various ways. All telecoms get access. There are SS7 signals that allow for porting or just momentary forwarding. Never trust SMS.
https://en.wikipedia.org/wiki/Signalling_System_No._7

I mean you can set up an MVNO, what I'm asking is whether an MVNO really has full control of their numbers or whether they can be misappropriated by the company that's operating the actual physical communications infrastructure

The right for MVNOs is based on the fact that US licenses spectrum to telcos and FCC requires carriers to offer access