I did some checking on the idea of using the windows desktop as a handsfree device for a cell phone. In other words, the PC acts like a headset, where audio output from the PC is sent to your cell phone mic, and audio input from the cell phone is directed to your pc speakers.
I found that the Widcomm Bluetooth stack includes a Headset service, and was pretty simple to set up to work with Text-To-Speech output.
Assuming you have the Widcomm stack installed, here are the steps:
1. Enable bluetooth on the pc and cell phone.
2. On the cell phone, search for new devices, and locate your pc. Add that device.
3. Next, scan the device for services and look for "Headset". Select this service.
4. On your phone, mark your pc 'device' as handsfree.
Now when you make a phone call, your cell phone should automatically connect to the pc as if it were an ordinary headset.
The only other thing you need to do is choose "Select Audio Device" from the NextUp Talker Options menu, and set the audio output device. On my system the audio device is named "Bluetooth Audio". Once this is selected, TTS output from NextUp Talker is sent to your 'headset' microphone.
The real trick to this is figuring out what Bluetooth stack you're using, and getting the Widcomm stack installed if you happen to be using the Microsoft stack. If you're using a stack other than Microsoft or Widcomm, you'll need to find out if the stack includes a headset service.
Some helpful links:
Finding Your Bluetooth PC Stack
Updating the Bluetooth stack on your XP Computer
This second link talks about bluetooth headsets in general, and covers how to switch from Microsoft to the Widcomm stack.