Fred Ramsdell thought a grizzly had wandered too close. Deep in the pine-scented quiet of the Montana wilderness, his wife’s shout pierced the calm. He froze, half-expecting to see a hulking shadow moving through the trees. Instead, Laura O’Neill came running out of their tiny teardrop trailer, waving her phone in the air like she’d just caught lightning. Ramsdell blinked. “No, I didn’t,” he said, certain she must have misread something. His phone had been on airplane mode for days; they hadn’t had a signal since Idaho. But Laura’s phone, perched on a sliver of reception, was lighting up like Times Square. “I have 200 messages saying you did!” she said, laughing and shaking her head. While Ramsdell, 64, had...