I have a love / hate relationship with my E71's 3G radio.
It's very fast compared with 2.5G / EDGE, almost as quick as our home WiFi, but it sucks power.
When I call or am called, 3G does sound a little better than 2G, but again it uses lots of power. If I'm using my headset the bottleneck for sound quality is either the headset or the Bluetooth connection so I can happily disable 3G.
Using CuteKeys, I can enable and disable 3G reasonably easily, but is there a way to enable or disable the 3G radio service for certain applications? So that I can restrict voice calling to 2G but let it use the 3G radio for data connections?