The digital music company Spotify, which uses free song streams to lure people to paid subscriptions, has earned the music industry’s approval by making money from listeners who might otherwise use their computers to download songs illegally.


In its shadow, another service, Muve Music, has quietly built one of the largest subscriber bases in the business by going after a part of the market that most digital companies have largely ignored: people who may not have computers at all.


Muve, a phone-based music plan sold through Cricket Wireless, offers unlimited song downloads for $10 a month, tucked inconspicuously into a customer’s monthly cellphone bill, which ranges from $55 to $65. In many ways its users defy the conventional profile of a digital music consumer. They are young and urban, yes, but instead of a laptop or a tablet, they use a phone for everything. Most earn less than $35,000 a year and lack credit cards, so they prefer Cricket’s month-to-month cash plan.


Since its introduction in January 2011, Muve has signed up 600,000 users, putting it in the league of Rhapsody, which has about one million subscribers, and Spotify. (Spotify has four million paying users in 15 countries, but has not said how many of those are in the United States.) And Muve is poised for another growth spurt with a new line of phones that the company believes could bring in millions of new users.


“Cricket’s customer is young, is ethnic, and tends to be middle and lower income,” said Jeff Toig, the senior vice president of Muve Music. “This is not a segment of the market that the major technology companies innovate for.”


Cricket, which has six million subscribers and is a subsidiary of Leap Wireless, will announce on Wednesday the introduction of a line of Android phones for $50 to $70 a month. These plans automatically include Muve, and are in addition to the Samsung, Huawei, HTC and other models on which Muve is an option. (In June, Cricket also began selling iPhones, but those do not include Muve.)


The major companies see Muve as a way to develop loyal customers in an area that had been an industry blind spot. Each month, Cricket says, Muve users download more than 70 million songs and spend more than 30 hours listening. By comparison, Pandora users listen for an average of about 20 hours each month.


“It’s a case study for how you execute a bundled music service,” said Stephen Bryan, executive vice president for digital strategy and business development at the Warner Music Group.


Among Muve’s advantages are that its primary customers — young, urban minorities — are some of the heaviest users of the Internet on cellphones. According to a study in June by the Pew Internet and American Life Project, blacks and Hispanics are more likely than whites to consider the phone their primary means of going online.


As part of Muve’s music licensing deal, a portion of the $10 monthly fee is earmarked for royalties, and divided among record companies according to each label’s share of downloads. Neither Cricket nor the labels would say exactly how much of that $10 goes to royalties, but it has been estimated by analysts and others to be $3 to $5.


For labels eager to license their music every way possible, that amounts to a steady income stream, if a small one compared with the hundreds of millions of dollars labels receive each year from retail giants like iTunes.


“Exploring these new opportunities and new methods of consumption is the one thing that’s enabling the music industry to weather the storm of piracy,” said Rob Wells, president for global digital business at the Universal Music Group.


But some analysts doubt Muve’s long-term potential. The service signed up 500,000 users in its first year, but halfway into its second it has gained only an additional 100,000. Cricket itself — a tiny competitor to giants like Verizon and AT&T, which each have around 100 million customers — lost 289,000 subscribers in its second quarter, the company reported recently. The company is hoping Muve and its new Android plans will help turn that around.


Walter Piecyk, an analyst with BTIG Research, said that Muve would have difficulty holding onto customers as Cricket moves its customers from the more basic feature phones into Android and other kinds of smartphones.


“They’re trying to increase the monthly bills of customers by selling them smartphones,” Mr. Piecyk said. “The challenge with that is that with smartphones you’ve got more choices for musical services. So they’re going to face increased competition with more mainstream music alternatives as they push their customers into smartphones.”


While bundling digital music services with phone or Internet plans has become common throughout the world, it is still relatively rare in the United States. Rhapsody, for example, is available as a $10 surcharge from MetroPCS, another small carrier that offers month-to-month plans with no long-term contracts. For Cricket, the Muve service, promoted heavily in its marketing and at its stores, has become an important way to distinguish itself from its competitors.


“This is providing an experience and more value to customers,” S. Douglas Hutcheson, the chief executive of Leap, said in an interview. “As we look at how to get sustained growth in the business, I think we’ve come up with an innovative, desirable way to do that, that’s something beyond just dropping to ever-lower prices.”