Notes: This code only works in Pokémon PLATINUM. It gives you All KEY Items (Including the Azure Flute). It adds 2 Pokémon to BOX 18 of your PC, so you may want to clear out BOX 18 before you apply this.
There's not any way to make the codes short, but there is an easier way to add new codes then tapping your DS screen over and over.
Notice: This process will delete all codes from your AR device. The codes it came with can be restored from the Code manager, but the codes you added yourself will not. You may wish to back these up first.
Download this file. This contains the cheat code. You don't need to open this file. Right-click this file and "copy" it. Then open up Action Replay DSi Code Manager. Right-click anywhere in the left column (the column that is labeled "Memory Card"). Then choose "Paste". Click "OK" on the following two dialog boxes.
And finally, Click "Commit Changes" to save the new code onto your Action Replay.
Once you turn on your AR with Pokémon Platinum in it, enable the code, and launch the game, You will need to PRESS the "L" and "R" buttons at the same time to activate this cheat.
This code will give you 10th Anniversary Celebi (2006), Toys R US Arceus (2009), and every key item (including the Azure Flute).
Just bought the AR DSi today and tested this code out. Hope it helps.