Does divorce occur via a mobile phone message, and what is the solution in such a case?

Sending a divorce in writing is a metaphor; divorce occurs if the husband intends it, but not if he does not intend it. So, if your son intended divorce by what he wrote, then his wife is divorced; but if he did not intend it, then no divorce occurs. His intention can only be known from him. If the divorce occurs before consummation, it is an irrevocable divorce, and a new contract is necessary to take the wife back.