The soon to be released iPhone 5 will be utilising a new SIM card standard. This means that you won’t be able to transfer an existing SIM from your previous handset into the Apple iPhone 5. Instead you will need to obtain a Nano SIM card, which as the name suggests has smaller dimensions than previous variations. The Nano SIM card measures just 12.3 mm x 8.8 mm.
Previously with the change to Micro SIM cards it was possible to use a cutter to modify your existing SIM. It is unlikely that this will be possible with the switch to Nano SIM cards, as it has been reported that they are also thinner at just 0.67 mm.
The adoption of the Nano SIM card standard means that Apple has had a bit of extra space available, when designing the iPhone 5. This has enabled them to make the iPhone 5 thinner than previous models. It is likely that we will see other manufacturers adopting this standard, as was the case with Micro SIM.