Curiosity. I didn’t study those things yet.
In: 2
The audio channel and signalling don’t always use the same route. A while the signalling channel will always go back to the provider to find out where to route the call I would be surprised If some networks cannot keep the audio local in the nearest cell. I.e. if both phones were on the same cell. But not 100% certain…
The call will go past the cell to one of the providers mobile switching centre servers (MSC).
If both of you happen to be connected the same MSC it will be taken care there.
If both of you are connected to differnet MSCs the call will go through between the MSCs.
They always go all the way out to the provider and back, even if the person you’re calling is right next to you. The routing does not take the shortest path.