This post seems say that they'd rather avoid the difficult programming challenges of working with the varied devices and protocols people use for communication generally, and just compete with other walled garden apps instead. I wish them luck, but it's a different trajectory than they were on a year or two ago.

There is (sometimes?) a way for Signal users to deregister from RCS which should presumably cause other devices to send messages via SMS instead of RCS.

People's Android devices can be opt in to receive messages via RCS based on phone number with either Google or their carrier. If the number is registered via Google, the number can be deregistered using a form. [1] For Verizon, it seems you can call Customer Support at 800-922-0204 to disable RCS. [2] Presumably other carriers have similar options.

Once RCS is disabled at Google/carrier level at the phone number level, other RCS compatible phones will fall back to SMS/MMS for delivering messages, which will cause the Signal app to be able to read messages via Android SMS APIs.

Seems like quite the hassle to set up an SMS app.

[1]: https://9to5google.com/2020/06/19/google-messages-disable-rc...

[2]: "How do I turn off Advanced Messaging" https://www.verizon.com/support/advanced-messaging-faqs/

Great context, though from an end user's perspective it was clear why and just left hanging with "find a new SMS messaging". The integration made adoption/integrating new users easier by allowing some to have one messaging app with progressive security for contacts on Signal.