hello,
I have the same problem with the mic... when i make a call, the other person can't ear me in good conditions but i can ear her very well.
My phone is a galaxy s4 (gt-i9505) with lollipop 5.0.1
The mic sound is very low that i can't make a phone call with zoiper... if i put my mouth near to the mic, in this case the sound is a bit better, but of course we can't make phone calls with the phone in a horizontal position.
Is urgent that the zoiper team make available a version with microphone gain control so we can continue using zoiper app.
I'm a zoiper gold... i paid for my version and for g729 codec and now i'm unable to use it.
I hope zoiper team could update the app very soon!
Thanks.