Set Infobox Delivery Option
This command is used to specify that a fax-on-demand document must not be retrieved by calling from a fax machine using line turnaround (one-call). The document can only be sent by placing a call to a caller-specified fax machine (callback). The command is the opposite of $nocallback. It is incompatible with the use of $fax_phone_last.
This command has no parameters.
Default: no restriction on document delivery method
Message Played: When this command is enabled, standard voice prompt 26 states that the image can only be received via callback if an attempt is made to select it in on-call mode.