In the past I have always been able to see if a infra-red remote control works (or a IR laser :-) by holding a digital camera in front of it and see the flashing of the IR LED on the screen.
However, after having purchased a TVB-Gone (which doesn't seem to work here....), I found out that the camera on the iPhone 4 and iPhone 4S don't pick up the flashing of the IR LED. How annoying. The Samsung Galaxy does still show it.
However, this is only limited to the main camera on the iPhone 4S! The camera on the screen-side still shows the IR flashes on the screen.