i've had my iphone 4 for over a year now and i'm not a heavy caller but compared to my work blackberry i notice that every call always sounds very digital and is often very hard to understand. I know (or i think!) its not a hardware problem as if i make a call over skype the quality is crystal clear, so I'm assuming its the network (vodafone), does anyone else find the quality very poor? any tips for improving it?