Answer: No, a bruteforce attack would most likely fail.
According to this site, and anyone who has ever been a mean big brother, there are only 10 times you can attempt to unlock an iPhone before it is completely locked and needs to be restored.
1-5 failed attempts - The phone will not lock.
6 failed attempts - The phone will lock for one minute.
7 failed attempts - The phone will lock for 5 minutes.
8 failed attempts - The phone will lock for 15 minutes.
9 failed attempts - The phone will lock for 60 minutes.
10 failed attempts - The phone will be disabled and will need to be restored.
So, as previously stated, 10 attempts will be your maximum. Also, Apple has released several new ways to set a passcode on your phone without having the use the 4 digit numeric code, which has a maximum of 10,000 passcodes (0000 - 9999). Users can use a 6 digit passcode which has a maximum of 1,000,000 possible codes (000000 - 999999), or even a phrase, which has a much greater number of possibilities for passwords.