The appearance of non-dispersive Einstein (¿rattling¿) modes, known as the phonon-glass paradigm in filled-skutterudite compounds, has been postulated as an origin of the high value of the figure of merit as well as the high heat capacity. However, very recent inelastic neutron scattering measurements by some of us [M. Koza et al Nature Materials 2008] on RFe4Sb12 (R=Ce and La) reveal the absence of rattling modes. Thus it would be very interesting to carry out a systematic study of the phonon modes in filled-skutterudites with different filling of magnetic R-atoms as well as with different transition and metalloid atoms to fully understand the nature of the phonon modes in these materials. We therefore propose to investigate the lattice dynamics of RPt4Ge12, (R=Ba, La, Ce) using the MARI spectrometer.