Hahaha! A boredom induced very thorough search through the registry, combined with google searches of every seemingly gps related item in there led me to a few very interesting discoveries. Most of all was the GPSOne driver. Research into that led me to this website which tells me that the GPSOne chip is responsible for aGPS. More specifically, it has 4 modes of operation (listed at the bottom of that page).

Now Standalone mode seems very promising for those of us trying to disable the stupid aGPS data charges we are getting. So I messed with the registry a bit, and I found it! The attached .cab file sets the GPSOne chip to Standalone mode I believe!

So here's the .cab file that I made that installs the registry tweak which I now have on my phone.

I have CONFIRMED on my own phone that it no longer tries to connect to medianet when I start up Garmin or any GPS program even though my phone radio is still turned on. Also, IM still connects, the gps still acquires a signal (after the minute or two wait we are accustomed to by turning the phone off first) and everything works perfectly, and I have 0 charges on my online bill! And my phone radio has remained on the entire time!!!

I do not have a data plan so have not tested any effects on medianet outside of aGPS and the IM's, but I only changed a gpsdriver so I can't imagine they should be affected in any way.

So there it is, others may need to test it still, but I'm 99% sure I finally disabled the stupid aGPS on this phone!

Cookies are appreciated! Or if you're feeling really nice you can donate from my signature to help me compensate for the charges I incurred while testing! (Optional of course!)    

I installed your cab file and it seemed to work. The first time I started it it DID connect to agps the 3g icon showed.
 So I shut off the device, and restarted it.
Started Garmin and it DID NOT connect to agps.
 I also tried google maps and same results.
It seems like you found the reg edit.
 I will try to connect again when I am in a different area.
I am not sure if the gps fixed my location with the agps the first time I started the programs.
 I will let you know... soon.

EDIT: Works great... I would have to give you a "That a boy" Cookie for your research.

Nice work, however there's no need for a registry tweak to modify the settings:

*On your phone, use File Explorer (show all files) to navigate to the gpsoneapp file.
*Click on it, select Menu/User Settings/Operation Mode
*Select your favorite mode.

Oh wow that's really cool! I think I'll stick with the .cab since uninstalling it will easily switch it back, and because I made it lol! Plus, this way I can group it into a .cab with all my reg edits at once for if I have to hard reset or anything. That's a great find though! Where did you find the gpsoneapp file? I would've guessed Windows\System\ but I don't see anything there. But yeah that way should work also. I'm not 100% sure, because it's possible I turned the driver off (the .cab does change the setting to 0). So does changing it to standalone that way work for you?

For anyone who might not be clear. To disable aGPS that way make sure you choose Standalone. You can check the Wikipedia site I posted to see what each option is supposed to do!

EDIT: Nevermind I found it....it's just under Windows, i just needed to have "show all files" checked.

The gpsoneapp is located in \Windows\
There are six possible modes in the "Operation Mode" menu, selecting the "Standalone" mode should prevent data from being transfered when running the GPS.

I'm using resco too, and I needed to use the built-in file explorer to open it.  For some reason resco doesn't show all of the files in the \Windows\ folder, and if it doesn't show the file it can't open it.

dangeorges, can you give more information on the various settings in the gpsoneapp?

brendan41357, you've misunderstood me: I'm looking for some documentation on all of the app's functions and settings, not just the operation mode setting (which the wikipedia article you found covered very well for me). 

oh brendan you little ....... hahahahaha you're the magic man 

you deserve a jar full of cookies.  geez, it's been almost one year since the incite came out, half-year ago when i joined this forum, this agps thing was a myth.

i'm glad we have people like you around here.

EDIT:  dangeorges, how did you know about the file in the windows folder? did you know it was there all the time?

I've known about the gpsoneapp since I got the phone.
I've never tested the modes, and it's possible, as you may find out, that changing these may not have an affect on the actual settings.

I went through the entire Windows folder and found some interesting applications there (e.g., att camera). Many work, some don't.

Before you ask, I don't have a list.

One way to test this app is to make a change, then check the registry, etc. The reason I've never tested it is because I have disabled all data for my account and never worry about charges.