The softening of acoustic phonons above the Peierls structural transition in quasi-onedimensional (Q1D) TTF-TCNQ organic crystals is studied. Unlike other papers, a more complete physical model is applied to consider simultaneously two the most important electronphonon interactions. The first is similar to that of deformation potential, and the second one is of polaron type. Analytic expressions for the phonon Green function and for the phonon polarization operator are obtained in the random phase approximation. The effects of interchain interaction on the phonon dispersion and Peierls critical temperature are analyzed.