Boku announced today that has raised $13.75 million in a new round of venture capital as it seeks to expand the range of carrier billing services it offers.

Based in San Francisco and founded in 2009, Boku has now raised a total of $91 million. The latest round includes many of the same marquee investors who have backed the company previously, including Khosla Ventures, Benchmark, NEA, Index Ventures, and DAG Ventures

“It’s a good vote of confidence in what is not the easiest funding environment,” said Boku CEO Jon Prideaux in an interview. “We’re obviously very pleased.”

The company did not disclose the valuation of the latest investment.

Boku’s growth shows how carrier billing, once a niche service mainly aimed at developing countries where credit card use is limited, has now gone mainstream. By giving consumers the ability to pay directly for content on their smartphones via their carrier bill, this type of billing system is gaining popularity with both consumers and phone companies.

Over the past year, Boku has gained momentum and announced a deal with Microsoft to enter the U.S. market. And though the company has not confirmed it publicly, Boku is now working with Apple and the iTunes Store in some countries.

That’s in addition to deals already in place with Spotify, Facebook, and Sony’s Playstation. The new money will be used to help Boku continue to deepen and upgrade the range of billing solutions it can handle on behalf of carriers and to keep up with growing overall demand, according to Prideaux.

The company is now operating in 70 countries with 250 carrier partners. It has about 110 employees. Boku’s competitors include Bango.

https://www.youtube.com/watch?v=ELoywnbdRk8

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