Zero went through a shit load of changes over the course of development.
I assume you're referring to the fact that it was originally planned for cell phones since I don't know any other major changes that occurred during its development. But if you read the post-release interviews and stuff they really give the impression that the cell phone game was little more than an idea that never really got off the ground. By the time serious work on the game started they had already switched platforms to PSP. Switching platforms in the very early stage of a game's development isn't that strange. The strange thing is announcing
the game while it's still in that stage.
That's what I pieced together from various sources, anyway. I didn't exactly save the links, though. The only one I found with a quick search was this
Type-0 was announced five years back, Kitase reminded, adding that he's happy to see it released. The game was in actual development for three and a half years, said Tabata, although there was a period where progress was at a bare minimum as he was working on a different project (The 3rd Birthday). He doesn't feel that the development was long, and wants to get to work on his next game.
Note the "actual development" distinction.