This is a brilliant, brilliant move by the Iranians. If it was chess it would be a !! move.
Japan is completely dependent on imports for it's energy needs. The last thing on earth the Japanese want is to trade for their energy needs with the pitiful Yen. As the dollar has devalued the Japanese have been busy sticking the knife in the Yen to keep it weaker than the dollar. The US and Japan are the top two economies in the world yet their currencies are dying. The Japanese have been using their dollar and euro loot to pay for their imports. Now all of a sudden they are looking at having to make the Yen an international currency.
Japan, through it's currency manipulations to keep the Yen weak, is responsible for much of the worldwide liquidity surplus by means of the carry trade (so dearly beloved by Wall Street) born out of the Bank of Japan's extremely low interest rates. If the Japanese raise the interest rates, a lot of big time finanicers and hedge funds managers are going to get very very nervous (to put it politely). The last time the BoJ did that in February the world stock markets almost crashed. Wall Street is already reeling from the subprime mess, and if the liquidity boom goes bust as well a depression is sure to follow.
This is also a kick in the nuts for the Europoodles for bowing down to US strongarm tactics yet again (by locking up Iranian funds in Euro banks). I bet Putin is laughing his ass off and Hu must have a secret smile as well. The US will predictably demand that Japan stops buying Iranian oil. When that happens China will move in. The US has been trying to strong arm China here too but it won't work. Since the European banks have frozen Iran's assests the Iranians will move the Yen holdings out of reach of strong arm tactics to Chinese banks. Of course Japan cannot allow China to build up a huge Yen mountain.
So this little letter kicks the Europoodles in the nuts, threatens the carry trade that feeds Wall Street and is yet another nail in the coffin for the dollar hegemony, and forces Japan to rethink it's entire currency strategy. And opens the door for China. Wow.