What is the ruling on swearing by Allah, during a fit of anger, not to speak to a friend on the phone, when one desires to retract that oath? And does sin result from it?

The anger that prevents the oath from being binding is that in which one does not comprehend what they are saying. If the anger is mild or moderate, and the Muslim comprehends what they are saying, then they must offer expiation for the oath if they break it, and they may speak to their friends [about it]; for the Prophet, peace and blessings be upon him, said: "Whoever swears an oath and then sees something better than it, let him do that which is better and offer expiation for his oath." The expiation for an oath is feeding ten poor people, or clothing them, or freeing a slave; and if one cannot find [any of these], then fasting three days.