Texts and Beeper rely on a service's publicly available access to bridge them to your universal inbox. When that option isn't available, they turn to backdoors and workarounds. That's what happened in Apple iMessage's case. To offer iMessage support, Beeper has a network of always-on Mac computers that are programmed to forward chats even to Android and Windows devices. Companies don't always approve of these methods, however, and when Beeper tried to hack its way into a simpler iMessage solution, Apple blocked it.

If you're curious and want to pay someone instead of spending your own time to admin it, check out Beeper which handles not only running the underlying Matrix instance, but also a bunch of bridges that let you talk to closed-source corporate messengers, e.g. WhatsApp, iMessage, etc. etc.