The FCC says cellular Data roaming should be just as available as voice and text roaming. We were the Debbie Downer a few months ago when we feared a roaming "brick wall" if smaller carriers aren't allowed access to data roaming at a reasonable rate. Of course, AT&T and Verizon Wireless have appealed this decision. Note they are the only ones.
It's very short-sighted of the top 2 carriers to oppose a friendly data-roaming environment but they probably need to appear to act like they have the interests of their stockholders in mind. The wireless customer wants to be able to roam almost anywhere, whether they actually use it or not. To be able to do so helps the wireless industry overall, no matter who owns the spectrum.
One of the difficulties in this area is that some carriers use different spectrum for data services and the FCC Order doesn't require carriers to support anything other than their own channels. This is part of the reasoning for AT&T's interest in T-Mobile. We're still heading toward the 6-band handset (or more!) being the standard for the US. Please, no bricks in my pocket.