Along with the spread of novel types of mobile phones such as smartphones, there has been increasing public interest in the health hazards associated with exposure to electromagnetic waves from these devices. Therefore, we estimated the specific absorption rate (SAR) of electromagnetic radiation by numerical simulation using a realistic computational smartphone model with an antenna for a third generation communication (3G) system (operating frequencies: 900 MHz and 2 GHz) and computational human models with the anatomical structures of Japanese male and female adults. We also assessed the relative variability of SAR based on holding a smartphone at various positions for data communications. The 10-g-averaged SAR (SAR _10g ) when the smartphone was operating at 2 GHz was generally higher than that at 900 MHz independent of the placement of the smartphone. Moreover, we found that SAR _10g had a tendency to increase when the smartphone was placed vertically in relation to the torso. In addition, it is possible that SAR _10g variability depends mainly not on placement height but on tilt angle.