[telebone_man]

I may be a bit late on this one, but here goes :)

It's technically feasible.. but in my opinion, if it's happened with you then it's very likely to be happening with others.

There's no one single way to setup telco infrastructure, so it would be educated-guesswork in the case of Google Fi.

Worth noting VoIP is real time, it either works or it doesnt. And if a call is being setup between two parties and it's otherwise a good quality call, then monitoring is unlikely to mark it as a bad call.

Personally, I would recommend logging this as a bug (if Google Fi allow it?) as I suspect it will be near impossible for them to spot these scenarios, even with clever monitoring tools.

I'll be keeping an eye on the news for follow ups on this one!