Hi @Vipin Joshi,
 
Because your U.S. and India accounts have different unique IDs (UIDs), they are currently seen by RingCentral as two separate, distinct accounts.
Therefore, direct extension-to-extension dialing is not natively supported between them. A call from the U.S. instance to the India instance will be treated as an outbound external call, and yes, if the India account uses local Indian numbers, it will be classified as an international call by the U.S. instance, incurring standard international rates.
The only way to enable free, seamless extension-to-extension dialing is to consolidate both instances under a single master account UID.