iOS 5: iPhone, iPad Wi-Fi Syncing

You’ll find the Wi-Fi sync option under the iTunes Summary tab

First, make sure you have iTunes 10.5 installed on your computer, and iOS 5 installed on your iPhone, iPad or iPod touch. To enable Wi-Fi syncing, do this:

• Launch iTunes 10.5.
• Connect your iOS device to your computer with a USB dock cable.
• Select your iOS device in the Library column on the left side of the iTunes window, then click the Summary tab.
• Now scroll to the bottom of the Summary view and check Sync with this iPhone over Wi-Fi. Of course, if you connect an iPad or iPod touch, iTunes will list that device instead.

With Wi-Fi syncing enabled you don’t need to connect iOS devices via USB 

Once Wi-Fi syncing is enabled, you don’t need to connect your iOS device to your computer to perform sync operations any more. Backups and syncing will happen only when your iOS device is connected to a power source, so you don’t have to worry about accidentally draining your battery when you need it most.

iTunes keeps track of Wi-Fi sync settings per device, so you’ll need to enable the feature for each device you plan on syncing wirelessly.