There are differences. If you have a plan in California, it works in New York. But if you're in Europe, good luck getting your unlimited data from France to work in Germany.
But aren't the users who need cross-continental/cross-country service the edge case? I would gladly trade-off inferior quality on a national scale for superior quality locally.
I guess if you enjoy getting off a plane and having no way to contact anyone, find a map to your hotel, and so on, this is a good tradeoff. For me, it's a terrible tradeoff.
Dont get me wrong I love having the capability you describe, but outside of the HN community I have to believe that the greater majority of users do not travel enough to justify national plans.
