Can someone explain what exactly roaming is. Is it when one carrier customer connects to another carrier?

I'm heading over to the grand canyon next week and I noticed on sprint coverage maps there is quite an area of gray (Roaming) on the way to the grand canyon. Will my curve show any indications if I am roaming???

It shoulde. On most plans these days theres no roaming charges in the US. I havent had to worry bout roaming in like 10 years or so.

Actually, I am grandfathered in a Northeast regional plan under Cingular now of course AT&T. 300 daytime and 5000 min night weekends. Roaming for me is if I go further south than Virginia I think I get hit for roaming per min. If you got a new plan chances are you don't need to worry about it. I just wonder since I have this calling plan would data usage be considered roaming if I go below Virginia? I been considering $10 more to get roll-over 450min but have not clicked the button to make the change yet.

I believe there is an indicator that shows roaming as a little blue triangle. It may be grey or another color, but I seem to remember the triangle in the top right area of the screen. I believe Sprint also has free roaming, but you may want to call customer service.

Does roaming included Data? When I'm roaming will I still be able to get on the internet through my phone's browswer or tether?

data yes, not sure bout tether.