Hi all,
In my opinion, the optimal spacing in between update letters should be about 1-2 months. Updates need to be significant and impactful so I try to collate them into one email instead of sending updates every week.
In addition, I am not a major proponent of calling since this might cause disturbance to the AO who is likely swarmed with work (20D cycle is ongoing now). Moreover, emailing will greatly facilitate the process as it will be easier for the AO to track our correspondence, update the Admissions Committee etc.
Hope this helps!