I said to my wife, "I will call your brother, and you are divorced today." Is this a divorce?

Divorce takes effect with this wording because it is an immediate divorce, and it takes effect at the very beginning of the day, based on the statement of Ibn Qudamah: "Whenever a time is made a ظرف (circumstance/container) for divorce, the divorce takes effect at the very first part of it, such as if he says: 'You are divorced today' or 'tomorrow'." There is no significance to his statement "I will call your brother" as long as he did not make the divorce conditional upon the call. The divorce would be conditional if he had said: "I will call your brother, and you are divorced when I call." In that case, it would not take effect except upon making the call.