iPhone comes with a number of ringtones that you can use for incoming calls, Clock alarms, and the Clock timer. You can also create ringtones in iTunes using songs purchased from the iTunes Store. Use the Ringtones pane in iTunes to select the ringtones you want to sync to iPhone.
Note: Charges may apply. Not all songs in the iTunes Store can be used to create ringtones.
A dedicated switch on the side of iPhone lets you quickly turn ringing on or off. You can also set iPhone to vibrate or not.
Setting Ringtones
In addition to the default ringtone, you can assign individual ringtones to people in your contacts so that you can tell when a particular person calls.
Set the default ringtone
From the Home screen choose Settings > Sounds > Ringtone, then choose a ringtone.
Assign a ringtone to a contact
From Phone, tap Contacts and choose a contact. Tap Ringtone and choose a ringtone. When that person calls, you hear that ringtone.
Setting the Ring Mode
You can switch between ring 
and silent 
mode. You can set iPhone to vibrate in either mode or both.
Note: Alarms that you've set using the Clock application still sound even when you set the Ring/Silent switch to silent.
Switch between ring mode and silent mode
Flip the Ring/Silent switch on the side of iPhone.
You can tell by feel if iPhone is set to ring or be silent. The Ring/Silent switch is aligned with the volume buttons when it is set to ring. In silent mode, the button is offset.
Setting iPhone to Vibrate
You can have iPhone vibrate when you receive a call. Separate controls let you sent iPhone to vibrate in ring mode, silent mode, or both.
Set whether iPhone vibrates
From the Home screen choose Settings > Sounds. To set whether iPhone vibrates in silent mode, turn Vibrate under Silent on or off. To set whether iPhone vibrates in ring mode, turn Vibrate under Ring on or off.