ENGLEWOOD, Colo.--(BUSINESS WIRE)--CSG Systems International, Inc. (Nasdaq: CSGS), a leading global provider of interactive transaction-driven solutions and services, today reported results for the quarter ended March 31, 2015. Key Highlights: First quarter 2015 financial results: Total revenues were $185.6 million. Non-GAAP operating income was $30.8 million, or 16.6% of total revenues and GAAP operating income was $21.9 million, or 11.8% of total revenues. Non-GAAP earnings per diluted share