The logo and other stuff can be changed with software like the Oxygen Phone Manager II and a USB cable: http://www.opm-2.com/OPM2/
Disclaimer: haven't tried it personally.
I dont know about the "7 - eleven" logo when you turn on the cell. The "SpeakOut" text on the main screen is not remove able but if you get a dark wallpaper ( black, dark blue, etc.) it will not appear.
I tried it and sure enough it did not appear! Thanks alot Kira.
No problem Apple!