I remember explicitly disabling acknowledging read reciepts on a sony ericsson in the mid-2000s because a friend of mine had discovered how to ask for them on their similar dumbphone and made dumb assumptions about how long until someone should reply.

No, it existed before the iPhone. It was actually weird to not have it on the iPhone, and I remember they were jailbreak tweaks to bring back the feature on the iPhone 3G.

> That's got to be pretty recent

Yes: only 20 years or so ;-)