Unlicensed Spectrum

Most private wireless systems cannot be licensed in the same way as cellular and other networks. Nobody would use a cordless phone if they had to apply for a license from the government, much less engage in a bidding war with their neighbors. Instead, regulators have set aside special frequency bands for which no license is required. To minimize interference, the transmission power of devices using these bands is limited to far less than that of a cellphone, restricting their range to at most a few hundred meters.

ISM

The ITU has designated several bands for Industrial, Scientific, and Medical (ISM) purposes, three of which are within the microwave region used by wireless devices. They were intended mostly for equipment that radiates microwave radiation as a by-product of its main function, not for communications purposes. Nevertheless, many cordless phones and wireless LAN systems have found them convenient.