The iPhone comes with some parental controls built in. Go to Setting>General>Restrictions
Guide for the above: http://knol.google.com/k/how-to-setup-parental-controls-on-iphone-ipod-touch-os-3-0-edition#
Or you can try this it cost $14.99 for the app but once purchased you can install it on any number of devices and all updates are free.
Anybody have a good program to parent control Iphone 4 and limit calls to contact list etc....? Have not found any that supports Ios 5.x