I know for a fact that AGPS is supported on the phone's radio. The XV6700 uses the Qualcomm MSM6500 as its radio chip. Googling for MSM6500 brings up
this which is an overview of MSM6500.
As you can see, aGPS is a BIG feature on it.
AGPS page
AGPS datasheet
What needs to be investigated is how this is exposed to the "outside world" i.e. Windows Mobile applications. I believe the API into the MSM6500's GPS module is secret, so we'd need to reverse engineer that. However the fact that fieldtrail.exe and/or calling 922 is able to alter the MSM6500 state machine to generate GPS co-ordinates is a huge starting point.
Also, we should collect all interested developers to one place to concentrate efforts ...