[lelanthran]

> Sometimes the call would be established and I would hear the other end, but the other end could not hear me.

I've done some work in this area - CGNAT is to be blamed when using UDP for voice traffic.

Very hard to reliably hole-punch CGNAT.

[mypalmike]

It seems unlikely to be a cgnat issue since the phone uses WiFi rather than cellular networks (where cgnat is most commonly found).

[codebje]

CGNAT is very common in broadband ISPs, to the point that you’re more likely to be sharing an IP with other users than not unless you’re specifically paying more for a dedicated IP.