How do you data roam?

[vMAC]

Can someone tell me how to data roam? I travel a lot and when I'm in areas where I'm roaming, I can't use data or even send txt messages they just bounce back. It seems that a lot of people say that in their area their service isn't good with Sprint and so they use Verizon or Alltel and roam on their EVDO; how's that possible. Where I live there is no Sprint EVDO but apparently there is Verizon EVDO. How would I go about roaming on their network for EVDO but calling using Sprint?