Although initially it was hard to get JIO sim but now its available and can be brought form Reliance Digital store. to find the store near your location use -> https://storelocator.ril.com/digital/
After using JIO for 2 month below is my review:-
Calling - If the call connects, the call quality is the best. JIO4VOICE app also gives a feature of video calling. Though calls are not connecting every time due to interconnection conflicts among the Telecom operators.
Internet Speed - Download speed is not that much effective all the day, but Youtube videos streaming works well. At night time good download speed is there. Below is picture of internet speed test.
Coverage - As of December 2016 in most parts of India, data speed might be slow, but signal is atleast there to receive and make calls.
Charges and Billing - As of now the service provided by JIO is free of cost.
Customer Service - I have not contacted them much but when I called received good support, if needed one can choose call back also but I had not used call back option.