Make sure your iOS is updated to the latest version, or at least to iOS 5. Then, make sure your iTunes is updated to at least version 10.5. At that point you can setup Wi-Fi syncing for your iPhone. Then, just follow these steps:

1. Connect your iPhone to your Computer

2. From iTunes:

• Open iTunes and choose your iPhone listed under devices in the left hand navigation

• Choose “Summary”

• Scroll down until you see “Sync with this iPhone over Wi-Fi” and click on that

• You can then choose to enable wireless syncing for your iPhone

3. From iPhone:

• While still connected to your computer, choose Settings>General>iTunes Wi-Fi Sync

• Choose the computer you have your iTunes setup on then choose “Sync”

Resource: OXSDaily