Before anybody outside Apple was aware of it, the project that would become the iPhone was referred to internally by the code name Purple. No one seems to remember exactly why; it may have been named after a toy purple kangaroo that belonged to one of the engineers.
Purple was so secret that even inside Apple hardly anybody knew about it.
It was developed in a lab sealed tight behind badge readers and a metal door. Employees had to sign NDAs for their NDAs. The lab became known as the Purple Dorm because people worked there round.