Smartphone is used widely by children and adults. Previous studies have shown that using smartphone can lead to certain struggles, especially for university students. However, there has yet to be evaluated on the effect of muscular pain while using smartphone in other age groups. The evidence gathered from this current study could be useful in preventing adverse health problems caused by smartphone usage in all age groups. The purpose of the study was to examine pain at the neck, shoulder, upper back and arm areas after smartphone use for 20 minutes. Smartphone was used in 3 positions during the study (on the chest level, on the table, and on the lap). Seventy-five asymptomatic users aged 10-48 years old were recruited into this study. The participants were assigned to use smartphone in random orders of each position. Location and severity of pain were measured by using a body pain chart and visual analog scale (VAS), respectively. The results showed that 1) After smartphone use for 20 minutes, pain at the neck, shoulder and upper back areas increased significantly and the pain increased in all age groups (p-value<0.05). 2) Office workers had higher pain significantly in the neck and shoulder; higher than high school and elementary school students (p-value<0.05). 3) Neck pain was found 164 times in the overall 225 studies, followed by shoulder, upper back and arm pain. 4) Neck pain showed the highest severity in the lap position in high school students, whereas it showed the highest severity of pain in the chest position level in elementary school students and office worker groups. 5) Smartphone use on lap caused the highest number of participants (96-100%) reporting pain in various regions of the body. In addition, using the device on lap led to the highest intensity of pain in the marked region, and also the highest pain level, overall. In conclusion: smartphone use caused pain at neck, shoulder and upper back areas in 3 separate positions in all age groups.