Buying new iphone

Unlocked iPhones bought directly from Apple will work fine. iPhones bought from places like Walmart, Target or BestBuy will likely be tied to a US carrier for activation and may not work with Indian carriers unless unlocked by a US carrier.

Do note, Warranty is not international, and will not be honored in India on a US iPhone. You will need to return the iPhone to the US for warranty service. Apple does not take international shipments for service.

Yes. It will work well on all cellular / mobile networks except the 5g mmWave network which will only work in the US.

Regular 4G and 5G should work fine however.

You cannot buy it from the USA Apple website and have it shipped to another country.