Can't they just brute-force it? It's a bloody 4-digit number (at least on my phone). How hard can that be? 9^4 equals 6561. A lot of tedious clicking, but hardly impossible even if you have to hire a human to do it, given a few days. Or do the Apple phones use some sort of feature to prevent that?
Several things about this: iPhones slow down passcode entries if too many false ones are entered sequentially; in addition, if too many passcode entry attempts fail, iOS may wipe the phone. The FBI wants Apple to provide them with a firmware that disables any autodeletion features and that additionally allows them to use WiFi or Bluetooth or USB or whatever to submit pin codes to the device electronically, bypassing the timeout mechanisms in the process.
Furthermore, it is unknown what exactly the passcode is. It could be a 4-digit pin; it could be 6 digits, or it could be
this.
I don't like this situation because either way, it can establish a dangerous precedent. If the FBI gets their way, that means the government can force corporations to give up access to private data (admittedly, this wouldn't the first time it happened. Even Swiss banks were forced to do that). On the other hand, if Apple gets their way, that means corporations can get away with denying government directives. I think the latter case could potentially be worse, as corporations are much less accountable than all but the most dictatorial of governments.
What the latter case
actually means is that corporations would be forced to build backdoors into their devices. This completely undermines their basic security, and is thus undesirable; You are endangering sensitive data of millions of people just to have a way to get at the data of a couple hundred. This is not a proportional response.
Secondly, consider that one of the minor points of contention between the US and China at this moment is the US' insistence that Chinese vendors should stop adding backdoors into systems shipped to the US. Do you want to live in a world where the US is allowed to do this, but everyone else isn't? Or worse, a world where no device can ever be considered trustworthy enough for sensitive information?