If you have an iPhone, open 'Settings' and then 'General'.
Next select 'Restrictions'. On/off should appear next to this depending on your existing preferences. You may need to add a new restrictions password if you haven't altered these preferences previously. Otherwise add the restrictions password created previously.
If restrictions haven't been enabled, select 'Enable Restrictions'.
Scroll down until you reach the 'Privacy' heading. Then select 'Contacts'.
Ensure that the slider next to allthings is slid to the right, turning it on. The slider will now appear green.