When a user logs an activity (a meeting or call), the meeting/call has been completed. The status should therefore equal completed by default.
Though this is logical, some of the detail behavior doesn't make sense. If I log a call as unreachable, then it should remain an open issue until the call becomes completed. But the user can change from the default (completed) to unreachable.
One can assume that this behavior will extend to other activity types.
And I go back to a circular conclusion... all activity types should have a single default and the user should make a choice about changing that single default.
Scheduled doesn't make sense as that default, so I would suggest the default be "open" to keep consistent with the UI labels for open activities.