A simple one-parameter generalization of the Schwarzschild spacetime was recently suggested by A Simpson and M Visser [2019 J. Cosmol. Astropart. Phys. JCAP02(2019)042] as a toy model describing the regular black hole and traversable wormhole states separated by the border (one-way wormhole) state. We study quasinormal modes of all the three states and show that the black-hole/wormhole transition is characterized by echoes, while the remnant of the black hole state is kept in the time-domain profile of the wormhole perturbation at the initial stage of the exponential fall off. Calculations of quasinormal modes using the WKB method with Pade expansion and the time-domain integration are in good agreement. An analytical formula governing quasinormal modes in the eikonal regime is given.