JIO full form 

Jio full form is Joint Implementation Opportunities. Jio is the LTE network owned by Reliance.  It also offers Voice over LTE or VolTE service.  The coverage of Jio in India is very good.  Everyone just says Jio, the Jio full form never used by anyone.  Jio network became a very popular network within a very short time period.

How to convert lte to volte :

Most of the phones these days are VoLTE enabled.  By default, the feature might be disabled.  To connect over the Jio network only give you data access. Still, the call will be via a regular circuit-switched network. These calls will not be free.