What model is your Bluetooth phone? This is going to sound like a pretty weak workaround, but since we are restricted by limitations of these devices, it seems only fitting that you use one of these limitations to your advantage...
What I've discovered about most Bluetooth phones (actually, every one that I've tested, but I haven't tested 'em all) is that they can only have one active Bluetooth connection. That being said, here's my solution. When you're using your phone for voice, use a Bluetooth headset. That way your one active Bluetooth connection will be used up and your iPAQ will fail to connect. Also, you get to use a Bluetooth headset
