For those who are saying the app doesnt work, reboot both iPhones after installation. The problem I had was the phones were connected, but no audio was being transmmitted. Rebooting fixed this - it works great now.
Id like the app to have a visual sound meter in a future version. And, perhaps a squelch knob to adjust the audio sensitivity to ignore softer background noises.
dkessler about Baby Monitor - WiFi & Bluetooth w/Background Audio, v1.1