How to use the bluetooth modem to make phone calls from outlook

Here’s my experience
I have a HTC touch diamond mobile and windows mobile 6.5 installed on it.
when I try to dial any contact from outlook via the bluetooth modem of my mobile, it calls, I mean the phone rings, and outlook shows “lift reciever and then press talk” message, but when I do this (while the other phone is ringing or have answered) it hangs up.