Preparation: If you are running iTunes 10.5 and have successfully installed iOS 5, there is but a single box to check in iTunes to set up Wi-Fi Sync.
iOS 5 for iPhone, iPad, and iPod Touch users now support Wi-Fi Sync, which means physically connect iOS device to Mac Book or Mac desktop to sync its contents with iTunes can be out-of-date some time later. Now you need only to be on the same Wi-Fi network for iTunes to see your device and sync it.
How it works:
First, connect your device via USB (one last time) to your Mac or PC.
Next, click on the device’s name in the left-hand list of iTunes. Make sure Summary is selected from the row of menu items along the top of iTunes and scroll down until you see Options.
Third. Check the box for the second option listed, “Sync this iPhone/iPad/iPod Touch over Wi-Fi” and click the “Apply” button in the lower-right.
Disconnect your device and the next time you plug it into a wall outlet, iTunes will initiate a sync over your Wi-Fi network. Do note that iTunes will need to be running when you plug in your iOS handset.
Either, you can sync an iOS device from your PC or Mac without the device plugged in. If you have installed new apps since your last sync, you’ll see a Sync button in the lower-right corner of your devices Summary page in iTunes. If nothing has changed since your last sync, you’ll instead see “Revert and Apply buttons”. Note that, click Sync and iTunes will sync with the device, whether it’s plugged in or not.
You may interested in how to sync videos to iPhone 4S for playing.