The use of ultrasonic velocity-attenuation in the transition region from glassy to supercooled liquid state of the (AgI)(x)(Ag4P2O7)(1-x) system is extended to the (AgI)(x)(Ag3PO4)(1-x) system. Comparison is made between both systems. The latter system is more liable to crystallize on cooling from the melt during sample preparation, possibly due to the more spherical shape of the Ag3PO4 molecule compared to the Ag4P2O7 molecule (allowing easier rearrangement of the molecule for crystallization with AgI). By deliberate quenching one can escape crystallization, but only for the x = 0.75 composition. Ultrasonics for this glass reveal structural features which are similar to those observed by differential scanning calorimetry.