BACKGROUND: Smartphones (SPs) are widely used by people of all age groups and genders. Users spend many hours per day on the SPs for different purposes, which imposes significant stress on their musculoskeletal system. OBJECTIVES: This study explored head forward flexion, lateral bending angle, and viewing distance while working with a SP in sitting/standing postures and one-handed/two-handed grips. The users' performance as well as pain development were also investigated. METHODS: Participants answered a questionnaire on pain experience before and after SP usage. Neck kinematics of 20 SP users were monitored by a motion analysis system while doing three tasks (typing, video watching, and reading) in sitting and standing postures. Performance was evaluated by number of typed words, amount of errors in typing, and total read words. RESULTS: The results indicated a significant increase in pain complaints in neck and upper limbs after test completion. Working with SPs in sitting and standing postures were, respectively, associated with greater head forward flexion for watching and viewing distance for two-handed typing tasks. Higher left lateral bending values were measured for one-handed watching and reading tasks in standing posture. The performance measures were superior for two-handed grips in all conditions. CONCLUSIONS: Overall, using SPs in sitting posture creates greater head forward flexion and lower lateral bending angles in all tasks and grip types. The findings of this study can be used to provide recommendations for SP users.