John W. Callahan was named president of Fidelity Investments Tax-Exempt Services, which provides defined contribution plans to higher education, health care and government organizations. Mr. Callahan, an 11-year Fidelity veteran, was executive vice president of sales and marketing for the tax-exempt services business. He replaces Guy L. Patton, who was named head of human resources at Fidelity and appointed to Fidelitys operating committee. Mr. Patton reports to Peter Smail, president of Fidelity Employer Services. Stephen F. Keating was named senior vice president of sales; he will take over Mr. Callahans previous duties.