I am vaguely surprised that phone messaging apps are not a two level architecture. level 1 the ui would manage your contacts and display and dispatch messages.

I am vaguely surprised that phone messaging apps are not a two level architecture. level 1 the ui would manage your contacts and display and dispatch messages. then you have a well defined interface and level 2, I guess you would call them plugins, knows how to authenticate you to to a service and deliver and receive messages. The messaging vendor would supply the plugin and the os vendor would supply the ui. Only vaguely surprised because, while this could be better for the end user and interoperation, it reduces lock in and who wants that? /s