[alistairSH]

But the user with the iCloud address is (probably) an Apple customer.

Similarly, with plain SMS, the cellular provider owns (some of) the infrastructure, but the user is a customer.

With Beeper, the customer is paying Beeper, but Beeper is using Apple's infrastructure (without paying for it).

[layer8]

I don’t understand your point. The user with iMessage that the Android user wants to communicate with is an Apple customer as well, and arguably pays Apple to be reachable via iMessage. And in the iCloud Mail example, the non-Apple user who is sending an email to the iCloud user also is not an Apple customer and doesn’t pay for Apple’s iCloud Mail infrastructure.

[alistairSH]

I was thinking two non-Apple users could use the iMessage protocol through Beeper. Maybe that's not possible?

[layer8]

I had addressed that aspect in my original comment (“Granted, …”).