Exhibit 16.1 Office of the Chief Accountant Securities and Exchange Commission 450 Fifth Street, N.W. Washington, D.C. 20549 June 19, 2002 Dear Sir/Madam: We have read the first three paragraphs of Item 4 included in the Form 8-K dated June 19, 2002 of CSG Systems International, Inc. to be filed with the Securities and Exchange Commission and are in agreement with the statements contained therein. Very truly yours, /s/ ARTHUR ANDERSEN LLP Arthur Andersen LLP Copy to: Mr. Peter E. Kalan Senior Vice-President and Chief Financial Officer CSG Systems International, Inc.