1. Yes. "Customizations" don't matter with Blackberries as configuration is handled by the service books which are automatically pushed to your BB when it registers on the carrier's wireless network.
2. Ask the seller. Don't rely on photos if the difference between midnight blue and black matter to you. There are plenty of photos where the Cingular 8800 looks black.
3. Warranty is generally handled through the carrier but Cingular isn't going to cover a non-Cingular device (no carrier will cover a device that isn't one of theirs). You should ask the seller about this as well.
4. There's no telling without knowing the specifics of the device that this place is selling but it's more than likely that differences are mostly cosmetic. As for themes, you can always load and/or unlock the ones you want so there's no reason to base your purchase decision on the supplied themes.
5. Upgrading the OS of the device can be done regardless of the carrier/prodiver of the device. You can load another carrier's OS so again, this isn't really a buying decision.
Originally Posted by tr4driver
Why not just buy it from Cingular for $450?
Maybe he wants an unbranded and unlocked device with BB Maps out of the box. Of course, that assumes that the information and photos on that site are 100% accurate. However, I'd say that it seems dubious to me. Again, I'd recommend verifying everything with the company selling the unlocked 8800 at the link given above.