Activation volumes (Delta V-A) and activation energies (E-A) are obtained for Ag+-ion motion in glasses in AgPO3-KI and ASPO(3)-AgI systems, from studies of the pressure and temperature dependent DC conductivities. In AgPO3-AgI glasses, Delta V-A and E-A both decrease monotonically with increasing AgI content whereas, in AgPO3-KI glasses, both Delta V-A and E-A reach maximum values before decreasing at high KI contents. This apparently strong coupling between activation volumes and energies is a new result, which suggests that free volume plays a dominant role in conductivity enhancement in these strongly doped glassy electrolytes.