1) Reliance Jio Internet uses 4G VoLTE ( VoLTE stands for Voice over Long Term Evolution i.e. Users can make voice calls over 4G LTE network , It is better than traditional switch circuits used by other Telecom Operators)
To define Technically, it uses Packet switching rather than Circuit switching
2) Uses your 4G Data pack of Jio Network (Internet) to make calls rather than your traditional way calling system . (Consumes data from your internet pack ) to provide HD Voice Calls and intrupt free network.
3) A Certain amount of Data is deducted for every minute when you talk with the recipient.(approximately 1Mb per minute)
4) Your mobile must support 4G VoLTE Technology or a basic 4G handset without VoLTE can use Jio4GVoice applications to enjoy VoLTE features.
5) Your recipient should also be in 4G VoLTE network to enjoy True HD calling benefits otherwise it seems like normal voice calling.
6) Reliance jio owns spectrum only in 4G band (unlike other operators such as Vodafone,Iidea, Airtel which also owns 2G and 3G band) , They are on 3 Bands (1800 Mhz, 2300 Mhz and 850Mhz)