Thanks for chiming in! But the problem I see here is that WA or iMessage (or whatever incumbent) needn't be fully open on a network. They can give themselves ac

Thanks for chiming in! But the problem I see here is that WA or iMessage (or whatever incumbent) needn't be fully open on a network. They can give themselves access to the open network, without fully opening up their own network to the rest of the network, and then by virtue of being the incumbent, thereby prevent better clients from taking off. (And that, of course, is the embrace & extend part. Once they're the dominant player again...)