Someone please correct me if I'm wrong, but "I think" if your phone is set to automatic, it will always find the best connection regardless of roaming status.
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it's the right time to crash, is it not?
You can go to Options >Network > Change to manual and scan for networks. If other networks come up try switching to them. If you switch and get service then you're good to go. If not, then you can't roam on that network.