iOS speaker problem with ANE using microphone

I am developping a language learning app which uses a native speech recognition engine linked with a Native Extension. Everything is working fine on the iPad, but on the iPhone speakers are behaving weirdly: the sound output goes to the phone speaker/receiver (the one used to make a call) so we can't hear anything.

I've tried several configurations:

When I play a sound in the app, and launch the ANE after, the sound output goes to the phone speaker, but the ANE has access to the microphone.

When I do the opposite, launching the ANE, then playing a sound, the sound output goes correctly in the loud speaker, but my ANE can't access the microphone.

I've tried setting useSpeakerphoneForVoice to true and using AudioPlaybackMode.MEDIA but it didn't change anything in both case.

Also, I tried to use the Microphone class, and when I initiate it and add a SampleDataEvent listener, everything is working better (sound in loud speaker and microphone working with the ANE) but on iPhones 4 and less sounds are garbled/scrambled and thus inaudible.

I'm using Air SDK 3.7 with iOS SDK 6.1.

Thank you for your help !