The growing interest in broadband wireless local networks and high trans- mission rates requires an increasingly reliable modeling of radio propagation channels, specially for indoor scenarios. The use of optical methods of elec- tromagnetic field tracking along (ray) trajectories between transmission and observation points, via high-frequency analysis of scattering by morpholog- ical constituents (obstacles) of the environment, such as UTD, fits well into the coverage analysis of corridors and empty rooms. While usual furniture dimensions are of the order of working wavelengths and disposed such as to render intractable the implementation of a comprehensive ray tracing mech- anism, the need arises for a hybrid method of analysis that allows for the matching of an UTD description of EM field tracking up to its penetration in a certain environment with the indoor scattering - by furniture and alike - analysis as carried out by the (numerical) FDTD method. This has been reported in the literature in connection with canonical two-dimensional sce- narios. In order to construct the building blocks of the extension of such a hybrid technique in order to encompass three-dimensional vector prob- lems as well, the present work addresses the application of FDTD to indoor coverage analysis. Starting with an in-depth review of the method and of its implementation with companion Perfect Matching Layers (PML), its application to coverage analysis of typical (empty) indoor scenarios is ex- plored and results are compared, both in time and frequency (via appro- priate Fourier inversions) domains, with those obtained via ray tracing, so as to validate developed numerical codes; a comprehensive review of UTD aspects and formulation is also listed herein. To conclude, a simple 3-D obstacle is inserted in previous scenarios thereby illustrating the adequacy of FDTD to consider the presence of furniture in the coverage analysis of environments of practical interest.