Phosphodiesterase (PDE) that catalyzes the hydrolysis of cyclic diguanylate (c-di-GMP) to GMP. Hydrolyzes c-di-GMP to GMP in a two-step reaction, via the linear intermediate 5'-phosphoguanylyl(3'->5')guanosine (pGpG). cyclic di-3',5'-guanylate + 2 H2O = 2 GMP + 2 H(+) Can function in vivo with either divalent iron or manganese occupying di- and trimetal sites. Dimetal is necessary and sufficient to catalyze conversion of c-di-GMP to pGpG, but conversion of pGpG to GMP requires an occupied trimetal site.