Is it permissible for the husband to speak on the phone with his betrothed wife before consummating the marriage, and is it permissible for the wife to exchange messages with her mother's nephew via Facebook in the middle of the night, and is the husband entitled to insult his wife and her mother's nephew based on Allah's saying: "Allah likes not the public utterance of evil, except by one who has been wronged"?

Your conversation with your wife over the phone is permissible after the marriage contract.

As for your wife's conversation with her male cousin, if it was impermissible, then you must advise them both, enjoin them to good, forbid them from evil, and prevent her from doing so in the future. You must not insult them, unless the insult describes their reprehensible action, such as "wicked" or "transgressors of Allah's bounds," as most scholars have held that it is permissible to insult a wicked person for the sins they have committed. So, you must advise them and explain their error, and it is permissible to be harsh in speech if that will be beneficial.