That’s the same problem they have with iMessage: you can watch this the first time you use a new number and it displays green at first but switches to blue once

That’s the same problem they have with iMessage: you can watch this the first time you use a new number and it displays green at first but switches to blue once it retrieves the other party’s key. That happens by connecting to Apple’s servers, which seems likely to be the same thing they’d do for RCS. Another function which is the same: you connect to the server to register your device to your account. It uses hardware attestation to verify that the hardware is what it claims, trying to make spammers have to buy physical devices and to prevent spoofing.