Hydrolyzes myo-inositol monophosphate. Catalyzes the dephosphorylation of GMP and IMP. a myo-inositol phosphate + H2O = myo-inositol + phosphate a ribonucleoside 5'-phosphate + H2O = a ribonucleoside + phosphate No visible phenotype during 5 hours of growth, decreased resistance to oxidative stress caused by diamide. Belongs to the inositol monophosphatase superfamily.