Will my cellphone work in the Philippines?

A short time back, Philip called me and asked if his cellular phone would work in the Philippines.

He told me that his network carrier in the United States is AT&T, and wondered if the phone would work in the Philippines.

Now, I am unsure. Does Philip mean will the phone itself work? In other words, can he put a local (Globe, Smart, etc) SIM in the phone and use it locally? Or, does he mean can he use the phone still on AT&T and can he roam on Philippine Networks? Well, it is hard to know exactly which of those he was

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