If you own an iPhone, you must maintain a subscription with a cellular service company to use many of the device's features. If an iPhone is disabled because of service cancellation, it will no longer sync with iTunes. If you still want to sync your iPhone with iTunes after it has been disabled, it must be reset first.
Turn off your iPhone by holding down the power button located on the upper right hand corner of the phone, then slide the red indicator to the right.
Press and hold the home button and power button simultaneously.
Release the power button when the Apple logo appears on the iPhone's screen. Do not release the home button.
Continue holding the home button until the iTunes logo with the USB symbol appears on the screen. This will take about 30 seconds.
Connect the iPhone to the computer and launch iTunes.
Select "Restore" when the iPhone control panel opens. Wait while the phone updates and syncs with iTunes.