If your iPhone is freezing or having other issues, DFU mode, also known as recovery mode, can help you get your iPhone working again. Please note that once in recovery mode, you will be able to restore your iPhone, but

you may lose valuable contacts, programs, MP3s, or other data. Keeping that in mind, use this as a last resort.

A known bug in OS X 10.6.5 can cause Macs to not detect an iPhone in DFU (recovery) mode. If your Mac is using this OS, then this process may not work. Try the same process on another Mac, or even a PC to avoid this bug. Some individuals do have luck using a USB hub (powered or not) in between the iPhone in DFU (recovery) mode and the Mac with OS X 10.6.5, so if you have a USB hub lying around, this is worth a shot.

First off, be sure to read through the entire process first to make sure you are prepared and know exactly what to do.

Entering DFU (Recovery) Mode

First, ensure that your computer is on and iTunes is running (having iTunes running isn’t necessary, but will save a bit of time later). Next, power off your phone by holding down the SLEEP button on top of the unit until the power off slider pops up. Slide your finger across the power off slider, then plug in your iPhone’s data cable to both the iPhone and the computer.

Next, Hold both the SLEEP and HOME buttons down for 10 seconds, then release the SLEEP button, but hold the HOME button for 10 more seconds. Your iPhone will have a blank screen, but should be in DFU (recovery) mode.

At this point, iTunes should detect a device in recovery mode and give you the option to resotre your iPhone. If iTunes doesn’t detect you iPhone, verify that you don’t have OS X 10.6.5 (see note above). If not, try the process again.

A few additional options to try if you are having trouble getting iTunes to detect your iPhone: 1)Ttry unplugging the USB cable and trying a different USB port, 2) Restart your computer and try again, and 3) Try a different data cable for the iPhone to computer connection.

Exiting DFU (Recovery) Mode

Exiting DFU (recovery) mode on your iPhone is a much easier process. Simply hold both the HOME and SLEEP buttons until the iPhone begins to boot up. Release the buttons, and that is it, you are back to normal iPhone operation.