For example, a customer who adds a line on the prepaid service can get 6GB for $40 a month, up from 3GB previously, and 14GB for $50 per month, up from 7GB. Prepaid customers have to pay in advance each month, instead of getting billed at the end of the month. All of the plans also include unlimited talk minutes and text messages.

The larger data allowance lasts as long as the customer maintains the service, Verizon said, and customers can bring their own compatible phone or buy one from the company. But the double data promotion will only be available for new customers to sign up for a limited time, Verizon said.

Still, some competitors do offer a better deal. AT&T gives prepaid customers 8GB of data for $40 a month.

The move to bolster the low-cost prepaid plans comes a few weeks after Verizon added a new third, more expensive tier to its regular monthly unlimited plans. Starting at $95 a month, the new tier lets a customer use 75GB of high-speed LTE data before facing a potential slower data rate.

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While Verizon (VZ) is the top provider of regular monthly wireless plans, it has lagged in the prepaid area. The carrier said that in the first quarter, it added a net 260,000 postpaid accounts but lost 335,000 prepaid customers. At the end of the quarter, Verizon said it had 111 million postpaid customers and 5 million prepaid customers.

By contrast, AT&T (T) reported 16 million prepaid accounts, including net additions of 241,000 in the first quarter. And T-Mobile (TMUS) added 199,000 prepaid accounts in the first quarter to build its total to 21 million.