[Gaelan]

There is literally no way for a non-active app on iOS to record without a red bar at the top of the screen. The only way that IG could possible get away with this is by somehow detecting that the phone screen was not visible and only recording then, but even then that recording would be imperfect, and somebody would have noticed. There is no way for the app to do what the author is describing.

[SentientNo4]

I believe the battery drain would be an even better indicator. I'm sure if an app would constantly do audio processing in the background it would dramatically lower the battery life.

[squarefoot]

It would not need audio processing in real time; using voice oriented codecs realtime transmission is totally possible without any detectable impact on data throughput. Take a look at Codec2's required bandwidth compared to the fidelity it offers. http://www.rowetel.com/?page_id=452