haha...very true! Actually when I tried this the friend who was with me said "I think you are completely insane". Well, now I know I'm not the only person to think of such a system I feel a touch better - especially as I am just a mere "newbie"
I've done a little more experimenting and it seems the signal strength and the specific network is important. I'm in Scotland at the moment and when I roam on orange (terrible indoor 3g coverage here) the signal is too low and the SIP call suffers badly from dropouts. However, when I use T-Mobile (full 3G signal in my house) the call is crystal clear. Also, it may just be my old equipment (PCMCIA BT card from 2001) but when I connect to the Nokia 7600 with bluetooth the port speed is obviously not high enough - I have to connect with the USB data cable.
Now the downside...to make a call I have to carry: Laptop, 3G phone, headset for laptop and chargers for them all. I suspect I might get a few odd looks walking down the street talking on that setup! B)