[bschiett]

major chip manufacturers probably have reference designs you can get, which include some of their parts, and which should be a good starting point.

you will indeed need to have access to advanced PCB fab and assembly subcontractor, but with some digging around you can find those.

the biggest problem is that you'll need hardware and software engineers who really know their job and can do the schematics, layout and firmware - doing a cell phone well is not an easy or small project, certainly not if you want to do something at a serious level and go beyond hobbyist type hacking.

you'll also have to do research on where to get an OS - developing this yourself is a huge project, probably just as big if not bigger than doing the hardware design. I don't know if it's possible, but perhaps you can get android OS source code and use that as a starting point.

you'll have to make each part of the hardware talk to the OS which means writing some driver or glue code, which is a whole other job. I'd try to use standard peripherals/ICs in your design for which android already has drivers.

without knowing more about your project, I can't really help more than this - if you want to talk about it feel free to msg me.