West Corp, an operator of call centers and conference calls, filed plans on Friday to raise as much as $500 million in an initial public offering.

The Omaha, Nebraska-based company was acquired in 2006 by a group led by private equity firms THL and Quadrangle Group LLC for $3.34 billion. A number of private equity-backed firms have begun to cash in their investments now that the IPO market is reviving.

West Corp provides conferencing services and other communications technology and services to a variety of clients, including hospitals, public safety organizations and corporations.

For the six months ended June 30, 2009, West Corp's revenue rose 12.7 percent to $1.2 billion over the year-earlier period, with net income of $57.1 million, according to a prospectus filed with the U.S. Securities and Exchange Commission.

West Corp will use the proceeds to paid down debt.

The IPO will be managed by Goldman Sachs & Co Morgan Stanley.

(Reporting by Phil Wahba; Editing by Gary Hill)