Apple has updated iTunes again. This iTunes update is designed to help sync your music in all of your iOS devices, automatically. You will need to have an iTunes account and need to turn this feature on in both iTunes and your iOS devices. Here’s how.
First, download the latest version of iTunes (currently 10.3.1 you may need to use the Software Update). Next, open iTunes. In iTunes preferences, go to the store and turn on the things (Music, Apps, Books) you want to sync.
Next, on your iOS device, go to Settings and tap Store.
You will see Automatic Downloads. Switch the settings to on to initiate the automatic downloads. Note that you can turn on Cellular to use the cell system if Wi-Fi is not available. However, unless you have an unlimited plan, you may incur additional costs.