Is it permissible to take a colleague's phone number without his knowledge to subscribe to a free SMS service and benefit from the SMS balance for myself?

A Muslim is not permitted to take another person's property without their willing consent. Free messages are exclusive to their owner, and their ruling is the same as that of money. Let a Muslim beware of being complacent in seizing the wealth and rights of others. Let him know that he will be held accountable for this on the Day of Resurrection if he does not seek forgiveness from their owner, for the Prophet, peace and blessings be upon him, said: "Whoever has wronged his brother concerning his honor or anything else, let him seek his forgiveness today before there will be no Dinar or Dirham, and if he has good deeds, they will be taken from him to the extent of his wrongdoing, and if he has no good deeds, then some of the evil deeds of his brother will be taken and cast upon him."