We are VoIP based (Telecom) C Corporation in NY, USA. Our one branch office is situated in India. But the employees hired to work for this company are paid through our wholly indian based group company only. We do pay all the US federal and State Taxes. So kindly tel us if we are liable to any indian taxation. And if they are falling under "US India Double Taxation Treaty" then how can we get the exemption?

The income earned while operating in India IS subject to India taxes under the U.S.-India Tax Treaty. You should be able to claim a credit for payment of those taxes on your U.s. corporate tax return.

In U.S. a citizen or resident must report worldwide income.
In India, a resident in India must report worldwide income. Also an India citizen who is not resident in India does not report worldwide income.
You can post any India tax related question at mytaxes - Index