List of
iPhones supporting Jio 4G and VoLTE
6, 6+, 6S, 6S+, SE and upcoming 7
5S, 5C only support 4G data. VoLTE is not possible on it as it doesn't have capable hardware. Jio4GVoice app is not yet available on iOS App store.
I have
iPhone 6S Plus and it needs to be updated to latest iOS version 9.3.5 after successful update, connect your iPhone to iTunes and you will receive Jio Specific carrier update message on your PC/
Mac and choose to install it on your phone. Although Jio VoLTE is supported from iOS 9.3.1, it is best to update to 9.3.5 for best compatibility. Update to latest version only if you don't mind loosing your jailbreak permanently and possibly forever.
BTW Jio VoLTE is working flawlessly on my iPhone and even LTE band switching is working well. The only irritation is if Band changes from Band 5 to Band 3/40, there is an annoying data consumed USSD message. The same behavior is observed on compatible Androids too.
I have another secondary phone Le Eco Le Max 2 and even that phone does reasonably good on Jio network.
Right now making VoLTE calls is a pain as 90% of calls to AVoId numbers fail. I have to call the opposite person 9-10 times
Jio Preview offer available for iPhones now. Just update your my jio app