I'm saying that I do not think it is possible to make the <ask the user> be a drop down field when it is a formula field.
So we move on to Plan B is to how to get your users to hand type either SP or GP in the box. ie how do we put up some help text on that <ask the user screen> they hit. Well there is not a way to put help text on that screen,
so we move to Plan C
Make a new formula field called
[Enter SP or GP]
make the formula just refer to your formula field that you already have. The only purpose of a duplicate fild is to give you a way to make a wordy field name like
[Please input SP for SP projects or GP for GP projects]
That way when the <ask the user> comes up there will be an explanation to the user. ie change your report to <ask the user> on this mirror field. and not the real formula field - just so that the <ask the user> experience has "help text".
