Yes, that is correct in the way it will work that if you're roaming and on a call, it will stay within that SID while on the call but as soon as you end the call, the phone will start searching for the native carrier again. But since Sprint's coverage isn't as elaborate or rural reaching as Verizon for example, when you start reaching the edge of Sprint's coverage, your call will likely drop and then your phone will start roaming and you can start a call knowing that you have a better chance of staying connected on the roaming network.