If you've forgotten your iPhone's passcode and it's either disabled from too many attempts or warning you that it will be disabled you don't have many options.
In the event this happens the only way to access it is to restore it with the last computer it was synced with, this will also allow you to reset your passcode. Please make sure you backup your
iPhone daily so you have the most recent data possible.
Note: This process will wipe all data from your iPhone. You will be able to put back your latest synced backup.
1. Disconnect the USB cable from the iPhone, leave the other end connected to your Mac/PC
2. Launch iTunes
3. Press and hold the Home and Power button on the top of the iPhone to turn off the device
4. Press and continue to hold the Home button while you reconnect the USB cable to your iPhone, this will cause the iPhone to turn on
5. Continue to hold the Home button until an alert message in iTunes appears that an iPhone in recovery mode has been detected
6. Now that the iPhone is in recovery mode, you must restore the device:
7. From iTunes, look under the “Summary” tab
8. Click on the “Restore” button within iTunes
Additionally, as long as you have a passcode set, if your iPhone is stolen it will have to be wiped out before it can be used again by the thief. Not a lot of comfort for a victim I know but at least your data will not be compromised.