Comcast has outlined details for the Xfinity Mobile cellular service it plans to introduce for current subscribers, with unlimited data plans ranging from $45 to $65 per month. As the new Xfinity Mobile service will use Verizon’s cellular network, Comcast will become a MVNO.  Comcast will sell handsets made by Apple, Samsung and LG.

Many subscribers will save money, especially if they don’t use a lot of data. The catch: Only Comcast cable Internet customers can sign up for the Xfinity Mobile service.

Comcast, which has nearly 25 million high-speed internet customers, said its wireless service is aimed at holding onto its customers. Comcast’s key competitors — AT&T’s DirecTV and Verizon’s FiOS — are part of companies with wireless offerings.

“We’re not getting into the mobile business to be the number one carrier,” said Sam Schwartz, chief business development officer with Comcast Cable. “It’s to benefit our existing core business. We’re not going to make billions of dollars in profit.”

The service Comcast is selling will be essentially the same as a Verizon plan, though Comcast will reduce speeds on unlimited plans after 20 gigabytes. Verizon’s threshold is higher, at 22 gigabytes, and reduced speeds apply only when there is network congestion.

Comcast will initially require customers to buy phones through the company. It’s offering iPhones, Samsung Galaxy phones and one budget model from LG. Customers can pay in full up front or in monthly installments, just as they would through a traditional carrier.

Comcast’s pay-per-gigabyte approach is similar to what Google is doing with its wireless service, Google Fi. Customers don’t need to guess ahead of time how much data they plan to use; both plans charge them only for what they use. With traditional carriers, unused data might get carried over to the following month; even if not, the customer still pays for the unused amount.

But Google Fi hasn’t caught on, in part because it works with only a few Google-branded phones and uses networks from T-Mobile, Sprint and U.S. Cellular, which aren’t as robust as Verizon’s. Comcast says it can also take advantage of vast array of marketing channels for internet and voice services.

Read entire AP story here.