The iPhone has included a Clock app with an alarm feature since it first debuted in 2007, however until recently the ability to wake up to a song from your music library has been conspicuously missing—a particularly odd omission considering that the older, traditional iPod models have supported this capability for close to a decade.
The good news is that iOS 6 finally delivers this capability, if only partially; in the iOS 6 Clock app, you can now choose a specific song from your music library to play when a given alarm sounds, however support for starting an actual playlist remains absent.
To set this up, simply go into the Clock app and create a new alarm or edit an existing one and choose the “Pick a song” option for your alarm sound.