• receiving calls, first-line customer liaison
• recording and tracking Incident and complaints
• keeping customers informed on request status and progress
• making an initial assessment of requests, attempting to resolve them or refer them to someone who can, based on agreed service levels
• monitoring and escalation procedures relative to the appropriate SLA
• managing the request life-cycle, including closure and verification
• communicating planned and short-term changes of service levels to customers
• coordinating second-line and third-party support groups
• providing management information and recommendations for service improvement
• identifying Problems
• highlighting customer training and education needs
• closing Incident and confirmation with the customer
• contributing to Problem identification

Source: ITIL Service Management, section 4.4.1