Can i buy an unlocked iphone from US and use it normally with my indian GSM carrier sim??

Be careful when saying unlocked without contract. They are two different types of phones. Unlocked means it is not locked to any carrier. Contract free means the phone is locked to a carrier but you are not locked into a 2 year contract because you paid full price for the phone.

Also note that warranty or support is only valid in the original country of purchase. So if you buy a phone in the US you will need to ship the phone to someone you know in the US to be taken in for evaluation. Apple do not accept or ship outside of the original country. The shipping will be at your expense.

That is indeed an unlocked iPhone but you will have to come to a US Apple Store to buy it and as you've been told you will have to return here for warranty service.