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.