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 iPhone 8
Both the phones have their pros and cons, Let's analyze both of them.
Advantages of Apple iPhone X :
1.Better RAM: More RAM means more applications can run at the same time,
2.Bigger Screen: more pleasing experience on a bigger screen.
3.Better Screen Resolution: sharper and crisper screen.
4.Has Dual Camera: Dual camera is useful in enhancing certain effects like blur, zoom and wide angle photos.
Advantages of Apple iPhone 8:
1.Has Fingerprint Sensor: It allows you to quickly unlock your device using your fingerprint and security to the handset
Verdict - In my opinion, Apple iPhone X is better in overall specs and price , if you need Fingerprint Sensor than going for Apple iPhone 8 makes sense.
You can also compare these devices on 91mobilesApple iPhone X vs Apple iPhone 8