So I had an idea

I know this probably isn't realistic, but what if smartphone companies gave you the ability to build your own phone? Imagine going to some companies website and being able to choose each individual part of your phone. How much it costs depends on the parts you choose. Want a bigger battery? Skimp on the camera. Want that quad core processor? Maybe take a smaller battery. You would choose the phone case that was made for a previously released phone. Imagine having an old phone you loved, but with updated guts. They could charge you the full retail price and maybe a little more for labor or something. I think it would be cool to piece together your own Frankenstein phone much like we do computers.