>It should not be possible on a cellular connection (because what's the point?),

It makes sense on dual sim phones, eg. sim 1 is connected to cell network, but sim2 doesn't have signal or is roaming.

https://preview.redd.it/9c70t7iluksd1.jpeg?width=1080&format...

https://www.reddit.com/r/Visible/comments/1fvbpun/wifi_calli...