You don't need to enable VoLTE. Insert the Jio (VoLTE enabled) in any slot. By default VoLTE will be active. If it is not, you can change the network preferences from Network option in settings.
5G technology is entirely new and still in testing face among telecom companies, device manufacturing companies, and software companies. Though rules of the 5G have been finalized, prototypes have yet not been finalized and phones in today's market will not be compatible with the 5G Technology.
Apple iPhone x does not support 5G and will not be compatible with it.
Apple iPhone never compromises in quality, so every time iPhone is better than the android phone... read more information why Are iPhones better than Androids mobiles?
Apple iPhone X vs Apple iPhone 8 Plus
Both the phones have their pros and cons, lets analyze them,as per the advantages .
Advantages of Apple iPhone X :
1.Bigger Screen:It will give more pleasing experience to watch movies ,playing games.
2.Better Screen Resolution:More resolution means sharper and crisper screen.
3. VoLTE Enabled; You can use this to make calls over 4G network. It is compatible with Reliance Jio.
Advantages of Apple iPhone 8 Plus:
1.Has Fingerprint Sensor :It allows you to quickly unlock your device using your fingerprint and more security to the phone.
Verdict - Both are great handset but in my opinion iPhone X would be great in overall and price,if you need fingerprint than go for iPhone 8 Plus
You can also compare these devices on 91mobilesApple IPhone X vs Apple IPhone 8 Plus
Check the video