How to Set a Sleep Timer on Your iPhone
You can set a sleep timer on your iPhone. If you like to fall asleep with music playing but don’t want to leave your iPhone playing music all night long, you can turn on its sleep timer.
Tap the Clock button on the Home screen.
Tap the Timer icon in the lower-right corner.
Set the number of hours and minutes you want the iPhone-as-an-iPod to play, and then tap the When Timer Ends button.
Tap the first item in the list, Sleep iPod.
Tap the Set button in the top-right corner.
Tap the big green Start button.

iPhone Glossary
FaceTime
Apple software that enables users with supported mobile devices to both see and hear each other during wireless conversations.

iPhone Glossary
iCal
Apple’s personal calendar application.

iPhone Glossary
iCloud
Apple’s wireless storage and synchronization service that keeps digital information updated automatically and wirelessly without user instigation.

iPhone Glossary
iOS 5
The operating system for mobile Apple devices released in June, 2011. With iOS 5, data updates and synchronization occur wirelessly through the iCloud.

iPhone Glossary
jailbreak
Altering an electronic device to remove default restrictions imposed by the manufacturer.

iPhone Glossary
Siri
A voice-controlled personal assistant application purchased by Apple and available exclusively on the iPhone 4S.