The Jio is a 4G service. Well, we are sure that you know this but it is worth repeating. If you have an older that only supports 3G, it may not work on your phone. Also, just to add, it won't work on feature phones. You need 4G connectivity and To make calls, Jio uses VoLTE network. This is something new for India. This means calls are made using data connection. Now, it won't be a problem for Jio to Jio calls. But for the Jio to GSM calls, which means calls to Airtel and Vodafone numbers etc, you will have to install an app called Jio Join because the calls will use interconnecting infrastructure that current telecom operators use. Even then there is a chance that many calls may fail.
