Well, for my old T616, I got bored during chinese school and I kinda scraped it off with a pencil. LOL. I felt kinda awkward using an AT&T Blue phone on Cingular.
As for my W600, I couldn't get the Cingular logo off of it, but I ended up getting an iPhone soon after they changed the name anyway.
Depends on what phone you have. For My w810, I had the cingular guy etched in the back battery cover, I bought a new battery cover with the walkman logo
http://cnn.cn/shop/index.php
for under $10