Elastic and relaxational properties of (NaPO3)((1-x))(Al(PO3)(3))(x) melts and glasses have been studied for x=0, 0.03, 0.06, 0.15, 0.60, and T=293-1433 K. Brillouin light scattering as well as ultrasound were used. The data were carefully analyzed using viscoelastic theory, with emphasis on the effect of added Al(PO3)(3), and on searching for a fast relaxation channel (besides the alpha-relaxation common to glass formers). The fast process is present for xgreater than or equal to0.03, and the T-dependence of the relative weight of both processes in the melts is derived. The replacement of Na+ by Al3+ increases the high-frequency LA sound velocity drastically, due to a twofold increase of shear modulus. Comparison with the shear viscosity is made. Viscosity and thermodynamic data are used for deriving an estimate of the size of the regions active in the slow relaxation process. Possible origins of the relaxation processes are discussed. (C) 2003 American Institute of Physics.