The Outgoing Calls settings allow changing how outgoing calls are handled. Touch the Outgoing Calls entry to expand the options as shown below.
Hide Number: The Hide number option allows you to place calls anonymously. This is equivalent to dialing *31/#31 (see Calling Features).
Outgoing Call Options: The Outgoing call options allows you to set your preferred default calling option: Use System Dialer, Use Call Through Service or Use Call Back Service. Once chosen here, this will be the default option shown on the Call screen.