Cable provider Altice USA is looking to shake up the wireless market in the US with a new offer that dramatically undercuts the competition. On Thursday, it said it will offer customers unlimited mobile service for just $20 a month. Even its non-cable subscribers can get in on the action for just $30 a month.

Altice Mobile will use AT&T and Sprint's networks to deliver its service. The company said the service will be available to people living in or near where service is offered by Optimum or Suddenlink, which are the cable and broadband brands owned by Altice. Altice sells high-speed internet, cable TV and telephone service under the Optimum brand in New York City as well as its suburbs in New Jersey and Connecticut. Suddenlink is the brand that serves West Virginia, North Carolina, Missouri, Arkansas, Louisiana, Oklahoma, Texas, Arizona, and Idaho.

The $20 a month (or $30 if you're not already an Altice customer) plan includes unlimited talk, text and data on mobile phones. It also offers unlimited international talk and text to 35 destinations and international roaming in those same countries. And the service offers unlimited hotspot usage and video streaming in standard definition to mobile devices.

The announcement comes at a time when the big four wireless carriers in the US -- AT&T, Sprint, T-Mobile and Verizon -- are aggressively competing to retain customers. Cable operators, like Comcast and Spectrum, have also entered the market. But Altice's pricing for unlimited service beats them all. A similar offer from Comcast's Xfinity Mobile and Spectrum Mobile are priced around $45 a month. Other prepaid offers for unlimited services from brands such as T-Mobile's Metro and Sprint's Boost are also around $45.

A different kind of MVNO

Executives at Altice say they're able to offer such a low-cost service because the MVNO, or mobile virtual network operator agreement, they have struck with AT&T and Sprint is different from the arrangement that Comcast or Spectrum has with Verizon.

The company says it has an "infrastructure MVNO" arrangement with its carrier partners that allows it to own and control the core network, which the company built itself. This also allows the company to own the SIM card. The way it works is that Altice uses the cell tower infrastructure of its wireless partners but then routes the traffic to its own switching infrastructure, which allows it to have more control over the call quality.

It's this technical difference that also allows the service to dynamically switch between using AT&T's and Sprint's networks depending on which signal is stronger and which network is more cost effective. The service will primarily roam onto Sprint but will use AT&T when roaming is required. If and when Sprint merges with T-Mobile, the company will also have access to T-Mobile's wireless network. Altice will also use Wi-Fi to offload some traffic.

By contrast, Altice officials say, this arrangement is different from MVNO deals that other cable operators, such as Comcast, have entered with Verizon.

Customers will be able to bring their own devices to the network or purchase them from Altice. The service will be compatible with Apple, Samsung, and Motorola phones, the company said.

Unlike other cable companies that have entered the wireless market, Altice has a lot of experience in mobile. Altice, which is based in the Netherlands, operates mobile networks in France and Israel. It entered the US market in 2015 when it bought Suddenlink and Cablevision. It then spun off Altice USA in 2017, but the company says it's retained some of the network experience from its sister company.

The biggest downside to the Altice Mobile service may be that it won't be offered nationwide. It only be available to customers who live in or around its 21-state territory, the company said.