It's unlikely to be taxing their production line all that much, but notorious ink-lovers ColorWare have announced they'll be offering custom versions of the iPhone 3GS. As with other ColorWare creations, the end result can be as tasteful or as lurid as your morals allow.
The usual range of solid and metallic colors are available, and you can have your earphones dyed to match too. The basic process changes just the back-plate of the phone, but you can also customize the normally-chrome bezel, the home button and the SIM holder.
Pricing starts at $150 for the back, then add $20 each for the bezel frame and button, or $15 each for the SIM holder and earbuds. Currently there's only the option to send in your own iPhone 3GS (in the US); ColorWare aren't offering the smartphone themselves at this stage.