Let the hive mind of Engadget get that for you.
"I just switched to Sprint from Verizon about three months ago for the Pre. Then I went for the Hero about a week ago. Now, I miss my hardware keyboard and am thinking about switching to the Moment. I am still able to switch back to Verizon if I want and get the Droid when it arrives. Should I just trade up to the Moment when it comes out, see if I like it, and if not switch to the Droid? Or something else entirely? Help!"
Yeah- I don't know what Darren's talking about. This was absolutely a setup feature & I remember debating it w/ my wife (whose phone it is). We decided to let it roam since T-Mobile's only letting you get unlimited data & we aren't planning on traveling out of the country anytime soon.