The country’s second-largest cable provider is looking beyond the set-top box for growth.

As smartphone usage continues to proliferate and cable subscriptions stagnate, Stamford-based Charter Communications is planning to launch its Spectrum Mobile service later this year. The move into the wireless market will pit the company against telecom giants like AT&T, but many observers still see the new initiative as worthwhile given its potential.

“There’s subscription revenue from monthly cell service, and it fits their model,” said David Souder, associate dean of graduate programs in the University of Connecticut’s business school. “It’s a growing market, so you can see their motivation to get into the mobile space.”