yes shadey you can de-brand and it runs on symbian 3^
youll need a list of product codes to match whichever market your in and a flasher... im with orange but have an unbranded handset so i got lucky... basically you change the product code to a genuine nokia code then update using Ovi this removes all branding as it updates to a nokia specific build
*edit*
a bit more digging found this
0599001: EURO1 BLU UK IRELAND (Blue Handset)
0598980: EURO1 DG UK IRELAND (Dark Grey/Black Handset)
0598997: EURO1 GR UK IRELAND (Green Handset)
0599006: EURO1 OR UK IRELAND (Orange Handset)
0598986: EURO1 WH UK IRELAND (White/Silver Handset)
if you want a full list its
here with all the carrier branding codes...
there seems to be a little bit of grey area about which flasher to us for S3^ i used to use NSS but it doesnt support S3^ handsets yet but it hasnt been updated for a couple of years so... ill leave that loose end there! if you can find a flasher let me know!