I don't think it would be unreasonable to require customers to have a really cheap mobile plan with no internet if they want to do calls outside of iMessager/WhatsApp/Messenger/etc.
This seems like a stupid idea on so many levels.
It's up to the network operator to efficiently manage their spectrum in a way that does not interfere with other radio users, and mutually between their own base stations.
If T-Mobile/Starlink manage to do that, you get additional connectivity in remote areas on your existing devices. If they don't, and their own network quality degrades, you can switch networks; if they degrade other networks' quality (actually, not just as a hypothetical), hopefully the FCC will shut them down.
This is an extremely power limited application. We're talking signals just above the noise floor here.
Think beam-steering MIMO WiFi where a base station can direct the vast majority of its energy directly toward a client, meaning clients in other directions never see the transmission and so the noise floor is lower and bandwidth higher. Similarly such systems can "see" which direction a transmission comes from and so distinguish multiple clients transmitting simultaneously - much the same way your eyes have no trouble seeing two people waving at you from different directions even if they're twins and dressed identically: the spatial information is sufficient to tell them apart.
To a rough approximation the delta between the theoretical limit and practical limit is computationally driven these days and we've gotten really good at the computation part.
> Access will be available "regardless of your carrier plan"
https://www.pcmag.com/news/googles-pixel-9-phones-get-their-...
That would not be possible, as neither access points nor clients are licensed to use nearly enough transmission power to bridge the distances required (and if they were, the spectrum would become usable for terrestrial uses).