You will be able to run any USSD that is supported by the currently inserted SIM(s) on your phone. For example, if you favorite 1 USSD each from Airtel Karnataka, Airtel Kerala and Idea Kerala and your SIM is of Airtel Karnataka, then you will be able to run USSDs belonging to Airtel Karnataka only. In case of dual SIM phone a small number on the dial button will indicate which SIM will be used to dial.