org-completion-use-iswitchb

org-completion-use-iswitchb is a variable defined in `org.el'.
Its value is

nil

Documentation:
Non-nil means use iswitchb completion wherever possible.
Note that `iswitchb-mode' must be active for this variable to be relevant.
If you decide to turn this variable on, you might well want to turn off
`org-outline-path-complete-in-steps'.
Note that this variable has only an effect if `org-completion-use-ido' is nil.

You can customize this variable.