Hey,
I also have the same Q. A friend of mine did get an iPhone 7 from the US and is using it in India. While there isn't anything that he had to do as of now, simply inserting the Indian sim and using the phone, however we dont know if the 4G LTE would work because its not yet available from the MSP in Ahm yet. It going to come out really soon though.
Fortunately / unfortunately, when my friend was getting his phone, he couldn't get it for me because the color I wanted wasn't available.
I have since enquired a lot of times (through friends, apple support, etc) and all have said the same, if you link with T-mobile you can use it in India, but they dont know if the LTE bands would be supported or not and eventually suggest to wait for the Sim-Free version.
I am in a dilemma whether or not to buy the phone just yet or wait until its available sim-free.
FYI, the iPhone is now available in India starting 7-Oct.