These are all the places I've found where Taxi Grab can be used to grab an item through a wall or object.

Useless or not, I've included it.

Taxi Grab does not work on PAL or XBLA.

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Isle o' Hags
----Plateau
--------Jinjo under the rock

Glitter Gulch Mine
----Main Area
--------Honeycomb under rock
--------Jinjo under rock

Jolly Roger's Lagoon
----Pawno's Emporium
--------Cheato Page you have to buy (only works the first time the room loads with it in the box)

Terrydactyland
----Main Area
--------Treble Clef under rock
----Inside the Mountain
--------Cheato Page behind bars
----Stomping Plains
--------Jinjo behind gate (might save a few seconds)
--------Jiggy behind gate (might save a few seconds)

Grunty Industries
----Waste Disposal Plant
--------Jinjo behind glass
--------Jiggy on other side of room in glass box (saves a few seconds)
----Outside
--------Jinjo behind wooden panel

Hailfire Peaks
----Lava Side
--------Cheato Page behind bars