This paper discusses the general suitability and possible limitations of an enhanced finite-difference time-domain (FDTD) simulation environment for straightforward and efficient RF design of complex transmitters. The study was conducted using a current commercially available multi-band mobile phone. Simulations were conducted in free space and with various dielectric loads, whereby different parameters were evaluated such as impedance, efficiency, far-field as well as near-field distributions of e-fields and h-fields, and the specific absorption rate (SAR). The results were compared to measurements. In addition, mechanical-design issues that showed a significant influence on the electromagnetic (EM) field behavior could be predicted by simulations and were experimentally reproduced. The accurate prediction of all essential performance parameters obtained by straightforward simulations suggests that appropriately enhanced software packages are suitable for device design in industrial research and development environments with few limitations, provided flexible graphical user interfaces (GUIs) and graded meshes combined with local grid-refinement schemes are available.