I bought jio sim 3 months ago, and it is necessary to install jio join in order to make free calls through jio sim if you dont have VOLTE supported phone, even though it is free to make calls through jio sim, the calling is very poor, if I call a person 10 times then only one call gets connected, its been more than 3 months and till now the problem is not fixed, So I wont recommend it for now