What is the ruling on using free internet available through a loophole in a telecommunications company's network, or which the company itself may have made available?

It is not permissible to change the mobile network to 3G if that constitutes fraud or deception against the company, due to the Hadith: "The wealth of a Muslim person is not lawful unless it is given with his willing consent." However, if the company permits it, then there is no harm, and it is necessary to refer to the company for inquiry.