Dialing a Bluetooth phone via serial AT commands?

I'm trying to control a bluetooth mobile phone via Max/MSP's serial object
for an installation piece I'm working on.

I'm using a Sony Ericsson k750i with a MacBook Pro and Mac/MSP 4.6.
I've confirmed that I can successfully dial numbers via the bluetooth phone
using BT-AT (http://mobile.feisar.com/phoneidentity.html)

I can send AT commands via the serial object to the phone, and it starts
dialling, but then hangs up.
There's no apparent difference between the AT commands that I send in BT-AT
and in Max/MSP, and I'm not getting any error messages
back from the serial object in Max, so it's hard to know what is wrong.

Is anyone aware of an example patch using serial to dial phones? I've
started with the serial help patch and the relevant example in the reference
manual, but am still stuck obviously :-)

Any pointers most welcome.

thanks.