Using Smart Phone displays in Raspberry Pi or other computers
Such LCD screens are often very difficult to use:


the connections are via a very small and flimsy flatcable
the intelligence is not in the display but in the main processor 
the interface is not documented
there are lots of different versions
on the electrical side, the interface often requires weird voltages and complex waveforms


The same arguments apply to the use of e-ink screens found in e-readers.

Note that the LCDs used in the older not-too-intelligent phones like the Nokia 5510 are sold and used a lot. These LCDS are black-and-white and low resolution (48x84), but they are cheap, easy to interface, well-documented, and there are only a few versions.