What is the ruling on purchasing a "Gray" device, which is legally prohibited in some countries, and operating it for international calls, knowing that the credits used are not stolen?

Using this device is not permissible due to the potential harm to telecommunications companies whose SIM cards are used in it, given the fees and taxes involved. Furthermore, laws enacted to serve public interest or protect private rights must be adhered to, as the ruler's actions regarding his subjects are tied to their welfare.