(Specialized Mobile Radio) The communications services used by police, ambulances, taxicabs, trucks and other delivery vehicles. Throughout the U.S., approximately 3,000 independent operators are licensed by the FCC to offer this service, which provides always-on communications similar to a walkie-talkie, but over a larger geographic area. Nextel Communications is known in this field for having acquired a large number of SMR operators and turning them into a nationwide system. See Nextel.