Again, I think you're confusing coverage areas with what roaming is. For example if you have Verizon and they have no towers in that specific area, you may be getting signal from AT&T towers, that's roaming. You can always check with your carrier and see if they cover the areas you're going to be visiting.
Now the strength of the signal, if any at all, in remote areas, well that's an entirely different thing all together.