you cannot unbrand the newer blackberry phones made after the Bold 9000 with available software. i did see a post the other day where someone had deleted certain cod files which did get rid of the carrier splash screen. but thats not a true unbranding, as the VSM file is still the carriers one, not ending in 000 (engineering) or 001 (unbranded).
Why debrand it? You can just unlock it and use it on any carrier. I have an Orange 9800 and have not had a problem with it. I am actually thinking of selling it to a Tmobile suscriber since this model will have 3G in the Tmobile frequency
Posted from my CrackBerry at wapforums.crackberry.com
Debranding totally is tricky and its troublesome. Its also not known if it works on the new 9800 but you can do a few things to make it look as if its debranded.
Next if you want to remove the printed brand on your phone, a nail polish remover or simply just use a cooper coin to scratch it off. Becareful, what I said may damage your phone so its your responsibility to take care.