If i buy a Virgin Mobile phone in Canada can i use it in the US?

i was looking at the virgin mobile phones on the canadian website and their phones are way better. if i buy a phone there can i use it in the US?If i buy a Virgin Mobile phone in Canada can i use it in the US?LoL no I tried that. I was going to buy a Canadian blackberry and when I called Virgin Mobile they said they couldn't activate it which I still don't understand...