I don't know if it was a total coincidence, but for the longest time my GPS would not work with my T-Mobile iPhone. But today, I installed two packages from Cydia, iLocator and Locatable. I don't know exactly what they do, but I ran them both one time and uninstalled them. From then on, my GPS works. I don't know if the apps "kicked" the GPS on or whatever, but all I can say is that ever since using those apps, my GPS works.