Your iPhone features the ability to select a customized ringtone or prevent your phone from making any sound when you receive an incoming telephone call. If you iPhone stops ringing, you should check to make sure your phone is not set to the vibrate mode and you have a sound associated with incoming calls.
On the left side of your iPhone at the top of the device, you will find a switch that you can use to activate and deactivate silent or vibration mode on your phone. If your phone no longer rings when you receive an incoming call, check to make sure the switch is set to ring mode. Look at the switch -- if you see an orange or a red bar, your phone is set to vibration mode and you should move the switch towards the display of your iPhone to activate the ring mode.
Check to make sure that your iPhone's ringer is not set to mute the sound associated with incoming telephone calls. Tap the "Settings" button and select the "Sounds" option. Under the "Ringer and Alerts" option, slide the indicator bar towards the speaker on the right to increase the volume associated with the incoming call ringtone. If the indicator is set all the way to the left, your iPhone is set to mute the ringtone.
Change the ringtone associated with your incoming calls in case the ringtone file selected has become corrupt and does not play properly when you receive an incoming call. Tap the "Settings" icon and select the "Sounds" option. Tap "Ringtone" and select a new ringtone. Your iPhone will play a sample of the ringtone to confirm your new ringtone setting. Press the "Home" button on your iPhone to save your ringtone setting.
Other Sound Options
Your iPhone also features the ability to play sounds when a certain predetermined event occurs. For example, you can program your iPhone to play a sound when you receive a new voicemail or new email, when you send an email, when you have a calendar alert, when you lock your device or when you press a character on your iPhone's virtual keypad. Tap the "Settings" button and select the "Sounds" option. Move the switch to the right of each sound option to the "On" position to activate the sound for that event.