This paper is situated in the context of heterogeneous integration of millimeter-wave communication circuits. It shows that VHDL-AMS models are well suited for the simulation of building blocks constituting an integrated communication system. Simplicity and reduced execution time are mandatory when it comes to the simulation of the behavior of an entire SiP. In particular, a VHDL-AMS model for RF MEMS capacitive shunt switches based on its equivalent circuit is presented. Subsequently, this model is, together with a transmission line model, applied to simulate the behavior of a mm-wave phase shifter employing RF MEMS shunt switches.