These Beeper folk sound a bit entitled. As was repeatedly mentioned in the other thread [1], building production applications on top of an undocumented and unsupported (in terms of backwards compatability, etc) API is a nightmare that should be avoided. Apple has every right to change their API, if they do Beeper will go down, and Beeper will blame Apple. I understand Apple's incentives to not want to be in this situ…
I'm deep into the Apple ecosystem and don't see myself getting out anytime soon. But I think their stance on iMessage sucks, even while understanding the strategic reasons they're doing it.
I don't see this as "leeching off an undocumented API" as much as demonstrating that iMessage is already in a state that allows 3rd parties to interact with it, documented or not. Every time Beeper starts working again, it shines a light on the fact that iMessage was never so locked down to begin with. It also puts pressure on Apple to answer the growing # of their own customers who are frustrated by the limits. These are good things, IMO.
Apple may have every right, but that doesn't make their stance good for the ecosystem or good for consumers. This is pretty clearly about forcing people to switch ecosystems and not about security. If security was the only issue, Apple could easily provide supported iMessage APIs that make it clear that the other user is not a verified Apple user, while still allowing interoperability.