Article is down, but if this is what I think it is... iPhones start increasing the time between allowed guesses geometrically after a few wrong ones, so this wouldn't actually work.
From the article (which is back up now, it seems):
> Not all phones are as susceptible to the R2B2's cracking. Apple's iOS, for example, increases the time between PIN attempts after each incorrect guess. But there is only 30 seconds delay after every five wrong guesses in Android phone
Then after the 30 second delay, if you guess wrong again, it goes up to around 5 minutes. The same happens repeatedly and it can get up to a few hours. I tried on an old iPod touch and got it up to around 4 hours.
However, it can be circumvented by restarting the phone.
