I have a Star W007 (for sale - see for sale on here).
It's to stop any signal conflicts - one SIM is on 3G, the other on 2G - means they can both have best signal reception/transmission conditions. If two 3G handsets are in close proximinity, the spread spectrum nature of the signals means you get a lot more bad packets.
It's a clever solution to the problem of using two 3G transceivers in close proximity.
The Star W007 is software-switchable in this regard - i.e. you can switch which transceiver module pairs with which SIM card.
+Steve
[size=2]Steve Gold
PO Box 1014, Sheffield S10 5YG, UK
Home mobie: Telefonica O2
Other UK mobiles: 3, Vodafone, Virgin
Foreign SIMs: Toggle (multi); Germany (Fonic); Poland (Orange PL);
Skype: stevewgold