Generally, the PU will vocalize the IFF. When the ball goes up shallow and high, the BU pointing up is to help the PU recognize that an IFF is likely, or at least possible. PU usually has better distance and angle to see if a fielder has ordinary effort to make this catch. It is not "declared" by the point only, but must be spoken. Of course, there are always exceptions, and BU should call it (if he is sure) when PU fails to do so.

The players can not hear your finger pointing to the sky. If you have your finger up you may as well loudly proclaim "infield fly, batter is out". Do it loudly. If the ball is near a foul line, add "if fair". Either umpire can call it, but if neither does it is still an infield fly if it deemed to be afterwards. Offense and defense should know the rule also. Don't call it too soon, be sure about it.

That's the FED rule, but not, I think, the OBR interp.

Bob's probably right on that one. I deal mostly in FED rules which is where my interp earlier came from.