The dynamic response of a Zener viscoelastic medium in the frequency domain is addressed. It is shown that, for low frequency, the elastic-viscoelastic correspondence allows a simple solution to Neumann boundary value problems for viscoelasticity. The dynamic solution is derived by an Indirect method of Boundary Integral Equations. For low frequency, the indirect BIE is established as a regular perturbation of the static BIE which has been studied by Pham (1967). Pham's solution is then extended to the dynamic case by perturbation arguments. A review of applications to inverse problems is addressed for the dynamic identification of a planar crack as well as an inclusion in a viscoelastic body. The method of solutions is based on the use of the reciprocity gap functional.