Actually your calendar status syncs to Teams but not vice versa. For example if a meeting in your calendar ends early and you manually change your status back to 'Available' in Teams, it doesn't change the synchronised status in 3CX - that will only change back at the scheduled end time of your meeting. Additionally if you make an ad-hoc meeting or call in Teams, this will not synchronise a status with 3CX as there is no calendar entry. Sadly because of this I find this sync largely useless.