I am not so sure if the GSM version will be launched in the US at all. If and when it is, it will be retailing at a price of about $500 if not more. Therefore spending an extra amount to get local warranty would turn out to be very much worth it.
However, it would do no harm to source it from the US, as we don't have any return or exchange policies in India. So if you don't like the phone all that much, then your only option will be to sell it. If you are OK with that, then getting it from the US might work out fine.
I am saying that you might not like it all that much, because people who have used the Motorola A855 have a love-hate thing with it. Either they love it too much or they cannot stop hating it. Check out some of the reviews on the net to know more.