Problem starting GSM dialup from bluetooth laptop

I have a sony ericsson k600.

The phone is successfully connected to my laptop using bluetooth and
most services work perfectly. I can initiate dialup from other devices
(e.g. my Palm Tungsten T) and this works fine on both GPRS and GSM.

I can dial internet using GPRS - *99***#.

The problem is that when I try to dial a GSM number using any telephony
device (Phone Dialer, DUN, Fax etc) - the phone starts to dial the
number and then stops - without reporting any error messages or
anything. The dialing lasts for about a second or so.

I have seen similar problems in other threads but can't find any
solutions.

Can anyone help?