The lattice dynamics of zinc-blende GaN and AlN were studied theoretically using a two-parameter Keating potential together with the long-range Coulomb interactions. Phonon frequencies transformed from those of the wurtzite counterparts were used to determine the two Keating parameters and the effective charge. We present for the first time the phonon dispersion curves for zinc-blende GaN and AlN. An interesting feature was found for the phonons propagating along the [110] direction, which does not exist in other III-V semiconductors.