Let understand both one by one.
4G Airtel offering you 4G LTE which means data get highest priority then voice and additional charges on voice as well as data. You will get 4G speed in some of the places. 4G is written on the signal but actual speed is not of 4G. Airtel also provide you 2G and 3G also so in this if you can’t get the signal of 4G then your data automatically shifts to 2G and 3G. Airtel charging you very high calling rates in comparison to all service providers. Airtel doesn’t have Pan India spectrum which means in whole India you can’t get network of Airtel.
4G Reliance offering you 4G VOLTE which means Voice over LTE means your calls getting the equal priority as data. When you are talking to someone on the phone and at the same time you want to check yours mail then you can check it. According to Mukesh Ambani Voice calls is completely free in jio. You will get 4G speed in every place because jio is only for 4G not for 2G or 3G so it means network never switched to 2G or 3G. It providing you data at very cheaper rates. Reliance have licence of Pan India spectrum which means you can get Jio network in whole India. Jio means Reliance 4G