Does divorce take effect if the wife contacts her sister—despite her husband's oath of divorce upon her if she does so—on the pretext of their father's death?

A husband's statement to his wife, "By divorce, if you call your sister, you are divorced," has two scenarios:

1. If the husband intended for the divorce to take effect immediately upon her calling her sister, then divorce occurs as soon as the call is made, according to the preponderant opinion. 2. If the husband intended that if she calls her sister, he will divorce her (a promise concerning the future), then divorce does not occur now, and she remains his wife until he fulfills his promise, should he wish to do so.