T-Mobile is going after rival carriers’ customers with an aggressive new offer promising to match or beat wireless discounts when eligible subscribers switch from AT&T, Verizon, or Sprint.

T-Mobile announced Thursday it will match discounts dollar for dollar via bill credits up to $15 for one line and $30 total for two lines or more, for customers receiving eligible corporate, affiliate, military or senior service discounts from the other major carriers. The discount match is in increments of $5, so T-Mobile says the new offer may actually beat subscribers’ current discount.

While the consumer segments are targeted, it could still apply to millions of potential customers. T-Mobile pointed to a survey from HarrisX Mobile insights that found around 50 million people have grandfathered wireless discounts from T-Mobile competitors.

New customers eligible for the offer must sign up for T-Mobile’s revamped T-Mobile One unlimited plan, now named ‘Magenta.’ The rate plan and discount stay intact as long as subscribers remain on the plan.

Pricing for T-Mobile’s new Magenta plan stays the same, but adds 3GB of smartphone hotspot or tethering per line and unlimited 3G tethering after that. Magenta also includes Netflix Basic for families.