Does your 'roaming' go by geographical area or network?

The way the digital licenses were sold in the 90's its almost the same thing, since spectrum in large geographic areas were auctioned off to the carriers. However there has been a lot of consolidation (like banking and casinos - the Sprint/Nextel consolidation being the latest). Now its usually based on your rate plan. And only in areas where your carrier doesn't have a footprint. That's becoming harder and harder, you really have to be far away from a city for one of the carriers not to have their own towers up.

But whether you are roaming still depends on your rate plan in the USA. My plan allows me to travel between Canada, USA, and Mexico and use my minutes toward any calls I send/receive (there is no roaming charges until I run out of included minutes).