Vontoo Inc., a once-promising Indianapolis-based technology firm that landed millions in venture capital but failed to meet growth expectations, has been acquired.

The company, which helps marketers send audio messages to thousands of phones and to track responses, was bought by Troy, Ohio-based One Call Now for an undisclosed price, the companies announced Tuesday.

Walter Meyer, president and chief operating officer of Vontoo, said the company currently employs seven people. Six will remain at Vontoo's offices in Indianapolis at 8606 Allisonville Road. Meyer said he anticipates he will serve in a corporate role at One Call Now. Vontoo has more than 1,000 clients. The retailer HHGregg and the Boston Celtics are among the businesses that have hired Vontoo.

Vontoo was founded in 2005 by local angel investor Bob Compton, who was involved in launching and supporting several successful tech companies, including Software Artistry, Aprimo, ExactTarget and Interactive Intelligence. The company raised more than $5 million in venture funding in its first three years and grew its work force to about two dozen employees but couldn't hold its footing during the recession.

In 2009, Vontoo announced a restructuring in which Compton temporarily returned as president and CEO. He expanded message delivery to other formats, including interactive video. Last February, Vontoo raised $192,000 as part of a $300,000 offering. In 2008, 11 investors chipped in $1.85 million.

Compton declined to discuss the reasons for the sale, citing a confidentiality agreement.

One Call Now bills itself as the largest message notification provider, using voice, SMS text and email messages. Its customers include businesses, schools, municipalities and volunteer organizations. Vontoo is the company’s third acquisition in 12 months.

“This acquisition expands our customer base in the education and business markets,” One Call Now founder and CEO Leib Lurie said in a prepared statement.