You can't do that. You will have to pay the cost of the monthly service plan here in the US, in addition to whatever you pay in your home country. The reason the phone is so "cheap" is because it's subsidized, and the discount purchase requires a 2-year plan with a data requirement. So, sure, you can take it out of the US, but your friend is going to get stuck with the bill.
I don't understand the reasoning behind doing this.