I feel that's not right either. Apple did not physically build the phone network and nobody is piggybacking on their network, Apple isn't hosting anyone's photos or videos afaict and the user pays for bandwidth, they maybe pay for notification relay to their own users.
It's more like phone manufacturer X that accesses Ma Bell's network creates phone with slightly better call quality that only works with other X phones and is worse with anyone else's phones. And they start doing that once they have >50% market share.
What type of infrastructure and operations do you think is necessary to handle 8.4B messages per day. So far, the cost of those systems and teams has come from hardware sales. The benefit is that it is effectively a paid for service and doesn't need external support from advertisers or by selling user data.
It really depends on what stack you pick and what kind of engineers you have. What's App famously used Erlang (an excellent choice for this) and was able to scale to astronomical levels with a fairly small engineering team and hundreds of instances.
It's more like phone manufacturer X that accesses Ma Bell's network creates phone with slightly better call quality that only works with other X phones and is worse with anyone else's phones. And they start doing that once they have >50% market share.