In a word, Yes! A "Gold Card" is a SD Memory Card that is specially modified specifically for, and unique to your particular phone.
YOU do the creating YOURSELF!
The "gold card", when placed in the phone causes the install process to by-pass the CID check stage during upgrades (etc) installations. It fools your phone to accept certain credentials of the ROM you are flashing/installing.
Simply put and relevant to you, your phone will think it is unbranded and will accept a RUU (Rom Update Utility) file meant for an un-branded phone. Once the RUU is installled your phone gets all the "soft" characteristics of an un-branded phone, i.e de-branded!
Like mentioned earlier, you have to (modify the sd card) create the gold card yourself and it is very easy to do.
A 1GB Crucial card worked fine for me, so you need to get a spare card, or simply use the one already in the phone. If you use your existing card, back up its entire contents to your PC/Laptop prior to commencing the creation process which involves re-formatting the card to Fat 32.
Some cards tend not to accept the mod, in which case, simply try another card. The simplest method I know of is with the use of a goldcard creator. See below.
I'm sure that by the time you've checked out various posts here and on other sites such as xda-Developers etc, you will be enlightened.
Checkout GoldCard Tool v0.0.5
. Instructions to create card are included in the zipped file.
Hope this helps.