Specifically hydrolyzes 7-methylguanosine monophosphate (m(7)GMP) to 7-methylguanosine and inorganic phosphate (PubMed:23223233, PubMed:24603684). The specific activity for m(7)GMP may protect cells against undesired salvage of m(7)GMP and its incorporation into nucleic acids (PubMed:23223233). Also has weak activity for CMP (PubMed:23223233, PubMed:24603684). UMP and purine nucleotides are poor substrates (PubMed:23223233). H2O + N(7)-methyl-GMP = N(7)-methylguanosine + phosphate CMP + H2O = cytidine + phosphate a ribonucleoside 5'-phosphate + H2O = a ribonucleoside + phosphate kcat is 0.24 sec(-1) with m(7)GMP. kcat is 7 sec(-1) with CMP. kcat is 0.07 sec(-1) with GMP. kcat is 0.04 sec(-1) with AMP. kcat is 6.2 sec(-1) with UMP. Monomer. Belongs to the pyrimidine 5'-nucleotidase family.