Richard Lai, the editor of Engadget China, reported yesterday a claim by the CTO of Hong Kong mobile phone operator PCCW that it is near impossible to cut existing SIM cards into the nano-SIM shape because the contact pins on current SIM cards are too big [and] will be damaged if a nano punch is used.
Then theres the fact that unlike the other standard SIM cards, the Nano-SIM is thinner, by 0.09mm. It might not sound a lot, but thats 12 per cent less than the micro-SIM in the iPhone 4S.
And unless you manage to delicately shave extra plastic at the back of the SIM card (known as the card body), it is unlikely to fit in the SIM slot of the iPhone 5.