By default, the iPhone rings for 20 seconds before sending calls to voice mail. In some situations, this amount of time may not be ideal. For example, if you generally screen your calls, you may wish for them to ring for less time. You may wish to extend the amount of time that your iPhone rings if you enjoy listening to your ringtones. Change the iPhone ring length if the 20 second default time does not suit your needs.
Begin placing a call by tapping the "Phone" icon on the home screen. Dial "*#61#" (omitting the quotation marks).
Note: "*" represents the asterisk key in the bottom-left corner of the keypad, and "#" represents the pound sign in the bottom-right corner.
Tap "Call." A screen will be displayed with the words "Voice Call Forwarding" at the top. Two lines below this, you will see a line beginning with "Forwards to" and ending with plus sign and an 11-digit number. Write this number down exactly as it appears on your phone and tap "Dismiss."
Tap the "Phone" icon again. Dial "61" followed by a plus sign (entered by holding "0"), the full number that you recorded in the previous step, "_11," another asterisk, the number of seconds (limit 30) that you would like the phone to ring before going to voice mail, and pound sign. When you are finished, the completed line will look something like "61+12345678901_11*30#."
Place the call. A message saying "Setting Activation Succeeded" will be displayed. Tap "Dismiss."