Essa é pros tecnólogos de plantão (só pra variar XP):

A comment on schedules:
 Ok, how long will it take?
   For each manager involved in initial meetings add one month.
   For each manager who says "data flow analysis" add another month.
   For each unique end-user type add one month.
   For each unknown software package to be employed add two months.
   For each unknown hardware device add two months.
   For each 100 miles between developer and installation add one month.
   For each type of communication channel add one month.
   If an IBM mainframe shop is involved and you are working on a non-IBM
    system add 6 months.
   If an IBM mainframe shop is involved and you are working on an IBM
    system add 9 months.
  Round up to the nearest half-year.

--Brad Sherman
By the way, ALL software projects are done by iterative prototyping.
Some companies call their prototypes "releases", that's all.