My first guess would be that you need a full-wave solver, and probably one with easily available body models. You may also be interested in time-domain results, so FDTD, FIT and FEM seem to be proper choices. Very efficient commerical software based on these methods is also available, that includes body models.
The literature is rich in this subject. The famous Brooks man uses both FEM and FDTD codes to solve for Specific Absorption Rate (SAR). I'm not sure if this is what your seeking? I will also tell you the existing codes are wrought with error, up to 200% error! So, you must really think about what your calculating and the required precision needed. If you are seeking to solve for the antenna field pattern, might I suggest GEMACS - this is a superior solver.