Up to 70% of Americans are paying too much for the cellular service, Consumer Reports found in a recent a survey obtained by Bloomberg. The reviews organization says that in some cases, customers are paying as much as $100 per phone line each month. However, with some savvy shopping, customers could cut their per-line costs down to $50 per month, according to the report.

Americans overpaying for cellular service is a two-fold issue, Consumer Reports told Bloomberg. For one, just 6% of wireless customers switch to another carrier, which suggests they aren’t shopping around to find better deals that may be available on other carrier networks. What’s worse, even if carriers offer better plans, they often won’t share those deals with their customers, according to the report.

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The wireless industry was once docile, with all four major carriers—Verizon (VZ), AT&T (T), Sprint (S), and T-Mobile (TMUS)—delivering similar plans and services. Several years ago, carriers often locked customers into two-year contracts. Device and plan pricing was nearly identical across carrier networks. Changing to other carriers also usually required switching numbers, which for many customers, was too much of a hassle for little gain.

Over the last few years, however, the wireless industry has become far more competitive, thanks in no small part to T-Mobile. The company, which dubbed itself the “Un-Carrier,” has shaken up the industry by announcing a rash of changes to its policies, including scuttling two-year contracts. The company also committed to paying off early termination agreements if customers switch to its service, and in a world of tiered data plans, T-Mobile offers a “Binge On” service allowing users stream as much content as they want from certain video services. Most recently, T-Mobile made another surprising announcement, saying that it would offer a buy-one-get-one sale on Samsung’s brand-new handset, the Galaxy S7.

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T-Mobile’s competitors have also made significant changes in the last few years. All four major carriers have nixed two-year contracts and now offer customers the option to pay for devices in monthly installments. Each carrier also sells handsets off-contract.

Meanwhile, they’ve actively targeted each other in ads, claiming to either have the best network, the best service, or fastest data speeds and offer special deals to steal customers from competitors. Indeed, the once-tame wireless industry has become vicious.

As wireless carriers morph their businesses by reducing rates and offering special, limited-time deals, Consumer Reports data suggests wireless customers are slow to react—and they’re paying for it. Part of the problem, Consumer Reports told Bloomberg, is that customers are not actively seeking out deals. And along the way, they’re letting too much cash go to carriers.

So, start watching your bill and looking for deals. It turns out that there’s money to be saved.