I need to know if anyone has tried upgrading an unlocked phone for instance I am a Cingular user using a TMobile 8700g and wanted to know if I upgrade my phone with a Service Pack Release from TMobile's website will this mess with my Cingular service? Will upgrading my TMobile phone lock my unlocked phone?

There is no way to re-lock an unlocked phone. All of the device software is written by RIM, and you can apply "T-Mobile" code onto a "Cingular" device. Just download and execute the program on your PC.

Then locate and delete "VENDOR.XML" on your PC C: drive (DO NOT MISS THIS STEP) and restart Desktop Manager.