[zGuy]

In all the upgrade threads out there, the conventional wisdom is to delete the file called "vendor.xml."
What about this scenario: If my 8900 is Rogers-branded Blackberry but I use it in the US with T-mobile's service, and I upgrade it with a T-mobile upgrade, should I keep the file vendor.xml?

[JSanders]

The vendor.xml file has no bearing on your chosen carrier... ONLY when loading an OS onto the device from another carrier other than the branded carrier.

If you are loading a Tmobile OS on to a Rogers branded device, you need to delete the vendor file. Otherwise, the OS may not even appear as an upgrade when opening DM.