This is more like market research. I work for a large company that has the tech to do this (we already have a demonstrator). We're more interested in what consumers think it should be. All companies base their decisions on what's called a CRD (Customer Requirement Document) that basically lays out what features need to be part of a product.

If your attempting to try this then I don't know how you would. I mean a phone can't export visual data through it's charging port or data port can it? As for the resolution just stick to whatever the phones is. You could always widen the projection if it came out small. I have my sinciere doubts about this though. However bluetooth has its ways.

If there was a projector that could hook up to your cell phone what size and resolution would you want? What would be acceptable?