I suffer from the same problem with an 8 month old RX300SEL and a V3.....doesn't happen all the time, but usually cuts the signal within the first 10 seconds, if you pass that period the call goes ahead as normal.
Never had a problem with a Nokia 6230, so I assume that it is a random compatability problem with V3's as I have pretty much everything apart from bluetooth switched off on the phone including the voice activation function.
Would be very interested also, if somebody has a fix!