The vibrational properties of InN samples grown by molecular beam epitaxy (MBE) technique have been studied using infrared (IR) and Raman scattering spectroscopy at room temperature. In the Raman measurements, the 532?nm (2.33?eV) line of laser was used as the excitation source. Lower branch (L-) of the longitudinal-optic-phonon-plasmon-coupled (LOPC) mode at similar to 430?cm-1 was too weak to be observed clearly in Raman measurements. It was however, strong in the IR spectra. A strong A1(LO) mode was also observed in Raman measurements and this mode together with the L- mode were used to calculate the electron effective mass in InN as a function of carrier density. In the theoretical calculation we used both the Drude and LinhardMermin models and obtained the electron effective mass in the range between 0.07 and 0.167m0 with increasing electron density from 0.79 to 2.8?X?1019?cm-3.