US version phone in India

Depends.

If your carrier in the U.S. offers an International Plan, you can use your phone under your normal plan for an additional daily or weekly fee.

If you don't have an International Plan with your carrier, the phone might still work OK on roaming, but you will pay a fortune in data charges.

Bottom line......check with your carrier before you leave on the trip.

It may not support the correct bands in use in India. If there is a problem with the device, the warranty is only valid in the US, and you cannot ship it back to the US, you would have to bring it yourself, or send it to someone you know in the US and have them bring it to Apple. Did you purchase an unlocked device? IF not, then you would have to get it unlocked by the carrier that has the lock on it.