TL;DR
- Users who have rooted their phone, have their bootloader unlocked or are using some custom ROMs report that their RCS messages are not being sent, even though RCS shows them as connected.
- The Google Messages app does not show any error messages when blocking RCS messages of these users and does not send the messages out as SMS or MMS either.
- Google famously campaigned for Apple to include RCS messaging in iMessage but is now blocking it for certain Android users.
This basically means adding the feature ourselfs and making our own build, not something we can name Android to give low level access to RCS in modem. This is feature we will just add.
Also on the side note, while in theory possible it will be a pain. We can’t just reinstall one package like modemmanger on typical Linux system, we must make a whole new builds for every device and apply patches again on every major Android update. While modem manufacturers do not even share documentation for them, just share a proprietary Android driver that should be in OEM system. So adding such feature means big reverse engeeniring, big effort for automatic patch and build system, all to support in my opinion already outdated and useless protocol which because it is already obsolete with standard XMPP or Matrix based apps.
Having built Android from source for several different devices, I’m accustomed to dealing with blobs and configs that enable access to each device’s hardware, including the modem. Custom ROMs generally just install the OEM drivers that came with the device, and let Android use them. That normally doesn’t involve reverse engineering.
I suppose it’s possible that RCS might depend on special modem features that somehow can’t be used like all the other hardware in the system, rather than just sending/receiving data over the network. (As I said, I don’t know much about RCS.) But it would be an unusual case. That’s why I’m a little skeptical. Since you haven’t given any references or supporting details, I can’t tell whether you have domain knowledge that supports your claim, or are just making assumptions.
Shrug… I guess it doesn’t matter, though, since time will tell. Cheers. :)
My background: have build some already done ROMs and spoke with some Linux mobile people about it :). Just to let you know, I also need some source to prove it, but having so little info how RCS works in floating in public non-specialized space is also telling something.