hi all..at&t was operational in india under partnership with a local service provider till 2005..can i use that sim card to work on my iphone for using the phone features??

No. Not possible. The iPhone works (without a "hack") only with the US AT&T SIM cards and to my knowledge not even with all of them.
Check for older threads regarding this.

yes you can if you legally activate the phone and go on roming (international calls)

i am talking with refernce to the puerto rico activation(watch youtube)..he has managed to use the old at&t sim card in his iphone

Puerto Rico is "in" the USA, even if it isn't one of the US states.

Roaming is indeed possible but for international roaming, you need a REGULAR iPhone contract from AT&T and this can't be done with an AT&T SIM (which wasn't even from AT&T but a partner) from India.

If ATT India has their own ICCID, the answer is "NO".

But if the ICCID is the same than the ATT and Cingular US , the answer is "yes".

But there is a problem, ATT is using Cingular GSM platform, is why the ICCID is the Cingular default.

This mean I doubt your ICCID match the Cingular one, the base of the iPhone unlock.

Just check it for us.

i dont think it's possible...coz we dont have any AT&T network in India or roaming partners... plus the SIM unlock The Puerto Rico one is not confirmed outside US..