Problem is with a current Android 6 Lenovo.
With speakerphone button OFF:
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No audio on dialing
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No ringing
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No hearing other person talking
-
Remote person can hear me (mike working)
With speakerphone button ON:
Default install. Have PC with Win 10 in same room - works fine (no issue with dialing, connecting, blocked ports, etc. Have Android 4.4 phone - works fine.
Possibly related:
http://www.zoiper.com/en/support/answer/for/android/11/SIP_-_No_audio_or_one_way_audio
(nothing seems to work)
Config->Audio->Audio Driver
to “External Java Driver” -- no improvement
http://community.zoiper.com/2671/zoiper-not-ringing-android?show=2671#q2671
http://community.zoiper.com/1434/android-zoiper-fails-to-re-connect-after-network-loss?show=1434#q1434
http://community.zoiper.com/2639/output-audio-microphone-working-android-vernee-speaker-fine?show=2639#q2639
Above 1+ed seems related.