Can cell phones purchased on AMAZON.COM be made usable by my provider?

I am researching new cell phones. And one of the ones I'm looking at will cost me $200.00 from the cell phone store. However, I see on AMAZON.COM that the phone (new) is available for far, far less than that. If I buy it from Amazon, can I take it down to the cell phone store and have them program it so that it's ready to go? Do they charge for that? In other words, will they slam me with fees for not purchasing their product directly from them?