Yes you can
I have a chocolate kg800 and I'm with AT&T (formerly Cingular). My phone is unlocked. However, I would advise using Verizon Wireless (the company that supports this phone) or considering a different phone because you may have issues.
Like, for example, I can be in areas with very strong reception, yet my signal is weak or non-existent, prohibiting me from making or recieving calls. Another bad thing is there is no speaker phone option, and the phone gives absolutely NO warning sound when the battery is about to die.
I also cannot match pictures with people in my contact list (so that it shows their picture when they are calling). Nor can I send pictures (via multimedia messaging; I don't have blue tooth). I've also had problems connecting to the computer via the usb cable.
Yea it's a sweet looking phone and touch screen is nice, and its also an mp3 player, but I think blue tooth is an essential to have with this phone.