The discount mobile service owned by T-Mobile said on Monday that it would offer 6 GB of high speed data each for two lines, along with unlimited talk and texting, for $60 a month. Adding additional lines with another 6 GB each costs $30.

The data allowance is up from only 1 GB per line previously at that price and undercuts competitor Sprint’s regular two-line plan with 6 GB per line by 40%, T-Mobile said.

The new offer is part of a recent push by T-Mobile to shift some price competition with Sprint from its own branded service to the low budget, prepaid MetroPCS service it acquired in 2013. Under CEO John Legere’s “uncarrier” strategy, T-Mobile has gained the most new subscribers in the U.S. market over the past two years and surpassed Sprint to become the third-largest carrier in the industry.

Sprint’s $100 per month, two line plan does not require that customers switch one or more lines from competitors, though Sprint does offer to cut 50% off the price of “standard rate plans” for people who switch from AT&T (T), T-Mobile, and Verizon (VZ). Sprint offers some cheaper plans for MetroPCS customers, but not the 50% discount that applies to T-Mobile’s main brand plans.

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MetroPCS customers use T-Mobile’s network but don’t have access to all of the benefits as regular T-Mobile subscribers. They can stream music from dozens of services, including Pandora and Apple Music, without counting against their data cap, like T-Mobile’s Music Freedom plan.

But they can’t stream video from popular services without using data, as T-Mobile subscribers can under the Binge On service. MetroPCS subscribers can choose to stream video at a lower quality level, as the Binge On service requires, to reduce their data usage, however.

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Shares of T-Mobile (TMUS) rose 2% on Monday in midday trading, while shares of Sprint (S) were mostly unchanged. Over the past year, shares of T-Mobile have gained 19% while Sprint shares lost 29%.