I want to use this topic because i see that leading admins are reading it. Everything that you guys do is great, but i would like to extend this topic a little bit and ask you if you are testing gps signal on 3g devices with redd00r. i sense that noone is doing anything about not working gps on our precious devices and you might just have the answer for all of us. my 3g is factory locked, jalied with redsn0w, hacktivated with ultrasn0w, baseband 6.15. my appologies if my question is not for this place.
Regards.
I read at ultrasn0w website that they announced on June 18 that they have successfully upgrade ultrasn0w to work on 05.13.04 Baseband, which is a real iPhone Baseband that actually has GPS working on it.
And redsn0w is also updated to be able to downgrade Baseband from 06.15.00 (iPad Baseband) into 05.13.04 (even though you never had 05.13.04 before).
So just simply do these steps:
1) Download the latest redsn0w (baseband downgrade available since 0.9.14b1)
Windows: https://sites.google.com/a/iphone-dev.com/files/home/redsn0w_mac_0.9.14b1.zip?attredirects=0&d=1
Mac: https://sites.google.com/a/iphone-dev.com/files/home/redsn0w_mac_0.9.14b1.zip?attredirects=0&d=1
2) Update your iOS to 4.2.1 (if you're already on 4.2.1, leave it there)
3) Download iPhone 3G 4.2.1 IPSW Firmware (you can find it on Google. download the stock one)
4) Open up redsn0w, click "Extras", and "Manual IPSW" (Not sure what it really written. I'm too lazy to check my redsn0w)
5) Choose the iPhone 3G 4.2.1 IPSW Firmware
6) Go back and start the Jailbreak
7) Uncheck Cydia (if you already have Cydia on your iDevice)

Check Baseband Downgrade
9) Start the Jailbreak!
*note: to do the step 6, you'll need to turn your iPhone 3G off*
Oh yeah, It's also written on Whited00r Blog:
http://www.whited00r.com/tutorial-downgrade-iphone-3g-ipad-baseband/If you iPhone 3G doesn't have any signal, try updating to the latest ultrasn0w. If it still doesn't work, reinstall both Mobile Substrate and ultrasn0w.