Hm...
I don't think, the iphone community is ready for such a thing.
They are kids without money, or arrogant yuppies, who know everything better.
Or kids without money, who know everything better (that's why they can tell you, why your free app sucks and is not worth the money)
It depends on the app and the audience.
I have no app, that could use it.
Today you find advice (good or bad) on the net within seconds...
On the other hand I just heared on the radio about a women, who is a "Life Adviser" (not even a psychiatrist or so) and talks to you per email and charges thousands of euros for that and some stupid rich bastards even pay her...
So your plan could be even working