First of all, this might not be the proper section, but still, the problem I'm referring to was solved on other devices using custom ROM.
I have the same phone and I have a weird problem. I can make skype calls but the sound is played through the speakerphone, and not through the earpiece. The same is true for other VoIP apps - Kakao Talk, Line..... When I tried to use Viber I couldn't hear the other person, yet they could hear me.
I read somewhere, that the same problem occurred with ZTE Blade and it was solved by using Cyanogenmod 7. So I guess this could be solved with a custom ROM.
Here's a link to a forum thread with people experiencing the same problem.