Chacham's Journal: Question: Cell phone in Poland for five days. What's best?

Someone i know is going to Poland for about five days, then spending the weekend in London, before heading back to the States. Having a cell phone is desired, so prices are being looked at.

In London, the cell phone is not such a high priority, so perhaps the price may decide against it. But, there is a real desire to have it in Poland (i think its mostly Warsaw).

The phone would be used to possibly call, but more likely receive calls from the States.

Anyone have practical knowledge in this area?