Purchased Jio SIM 2 weeks ago. First, calls were not working inspite of full signal strength. The prepaid card vendor says I have to upgrade the OS on my phone in order for it to work. I did that then calls work, but network is very, very poor. Calls break and voice is garbled, even the customer care people admitted that. Data doesn’t work no matter what you do with the settings. Have complained twice but nothing happens. No backward compatibility available, so 4G sim does not work on 3G. Every other operator’s 4G sim works on 3G also. No clarity on how Jio SIM will work, company does not provide.