I'd argue if it was completely incidental then it's network effect. If it's deliberately done to achieve anticompetitive outcome it's more than that. In the case of Apple, we know they do these things for anticompetitive reasons. They are on the record in email chains discussing how they weaponised iMessage in exactly that way. So I think they don't get the benefit of a benign assumption here ... it's more than likely they are specifically doing this as a way to drive a wedge that forces people into their ecosystem against their will.
yes, and? (edit: well, actually, no, you're just ignoring the lock-in part. but even if so,) in this case, it's a network that's more limited than others in terms of who's able to access it and what hurdles they have to overcome. like, network effect can be pretty bad, but this, mixed with ecosystem lock-in, is even worse.
