I could see Fallout 1 and 2 working, but even then they are pretty extensive in terms of memory. Fallout 2 alone is like 1(1/2) a gigabyte.
You mean storage (as opposed to memory)? Most smartphones nowadays have a lot of storage. If you could find a way to compress the game assets (images, etc.) down a little, which would be fine for a smaller screen, it should be fine. Fallout 2 should easily run on current-gen smartphones...both in terms of memory and storage.
I see no way in hell that 3 or NV would work.
Agreed. Even if they scaled it back to run on a smartphone I'd never play a first-person game with such an involved UI on a phone touchscreen.