Are there any handset codes/ reg. hacks for call sample rate

[Guest jordy]

Most Nokia handsets have a code foe enabling/ disabling efr. Is there any way to change the sample cate for voice calls on the SPV?. Asking because, as we know, the handset buzzes on voice calls (through the headset as well) - but seems fine with non radio sources such as MP3 and Mpeg files etc. I don't know much about this but would a better sample rate clean up the call quality...

Cheers,