Audio [Q] Bluetooth 3.0 vs. 4.0 Headset profile difference?!

Hello forum,

I'm using a Jabra Supreme bluetooth headset with my Galaxy Note 2.
When I'm making a skype / VoIP call, the sound quality is excellent. When I do a call to the same number via regular cellular connection however, the sound quality is less than mediocre (and also worse than without the headset).
Does anyone know why that is like that?

I'm assuming that the phone uses different bluetooth profiles for cellular connection, and when I'm doing a voip call.
But it should be the same profile (HSP). It can't be A2DP, because the sound transfer one only goes one-way. The only other possible profile is "Hands-free-profile".

The headset supports bluetooth 3.0, whereas the Galaxy Note 2 supports 4.0. Is it possible that the audio quality under the HSP profile with bluetooth 3.0 is lower than with bluetooth 4.0?

Anyone any ideas?