The issue dates back to a decision by AT&T years ago to phase out an older wireless network that BMW uses to communicate with its customers’ cars. BMW’s system automatically notifies the car-maker in the event of an accident and lets drivers request help with roadside problems, such as changing a flat tire. Now AT&T is ready to shutter the old network in favor of newer mobile technology.

Owners with affected systems can get a free retrofit from BMW, but those who ignore the situation could find themselves with unconnected cars in an emergency. Models that must be retrofit include all 2013 and earlier models, 2014 X6 SUVs, 2015 and earlier X1 models and Z4 cars from 2016 and earlier, the Wall Street Journal reported on Monday.

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AT&T (T) said it first announced plans to sunset its second-generation, or 2G, wireless network in 2012. Starting next year, the carrier wants to use the same airwaves to expand its higher speed 4G LTE network.

“Reallocating capacity to our more advanced wireless networks will help more of our customers have a better experience,” AT&T said in a statement. “Adding spectrum and managing our existing spectrum for its most efficient use provides customers with the best wireless experience.”

But with smartphones nearly ubiquitous, many don’t use BMW’s emergency service, which is provided free for four years with its new cars. Customers who don’t want the retrofit can get a $300 voucher for BMW accessories or a $200 Visa gift card, the company told the Journal.

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The transition doesn’t affect more complicated connectivity features that run over AT&T’s more modern network, like BMW’s ConnectDrive service that can provide a wi-fi hotspot in some models.