> Similar to how Nextels cellular "push to talk" fake walkie talkies worked.

Not really. The reason the PTT was virtually instant connect has nothing to do with optimization tricks, but rather is a purpose built design of the network tech it was using.

Nextel PTT didn't go over a normal cellular network, it went over something called iDEN[0]. iDEN provides a trunked radio service[1] which has a similarish feature to a conventional two-way radio. Sprint acquired Nextel and as iDEN wasn't as relevant anymore with the advances in cellular networks (despite those who actually used the PTT functionality), in 2013 Sprint shutdown the network to use it for additional LTE bandwidth in the 800mhz band[2].

[0] https://en.wikipedia.org/wiki/IDEN

[1] https://en.wikipedia.org/wiki/Trunked_radio_system

[2] https://en.wikipedia.org/wiki/Nextel_Communications

No, PTT would send audio from the caller without the receiver accepting anything, but it wouldn't send anything from the receiver without action on the receiver end.

It was obnoxious at times, but very different than the kind of privacy invasion that the receiver's sending data without active involvement is.