Hard to use Amazon in the Phils Ian, it can be done I believe but it's all external to the Phils, using international couriers.
I presume the other one you mention is Buy.com?
Never heard of them before and after a quick look at the site it would appear they are just a 6 country operation so far.
Lots of big online companies are reluctant to do business in the Phils probably because there is still not the appropriate critical mass of viable credit card holders, i.e. people with good enough credit to be able to buy online easily.
Logistics are still a bit ropey too.