Big carriers roam onto smaller carriers' networks and vice versa. That and there are networking companies who own cellular towers, but lease them to major carriers for roaming revenues.

Nextel's network is actually pretty good. Texting does a take a bit longer because you have to download the message, but I don't text much, so it's all good.

Also, when I take the bus/train, I notice how I am the only Nextel user in the pack, which means in my area, my network is not as crowded as other networks. Although, I know that Boost Mobile caused the iDEN network to become flooded with people because of their unlimited plans. But now they offer CDMA phones on Sprint's CDMA side, so it's easing up the burden on iDEN.

Overall, I really like iDEN. It's a good technology.