A radio transceiver suitable for use in a mobile telephone is provided. The transceiver is operable in dual modes so as to be able to operate with both GSM and UMTS systems. In a preferred embodiment the transmitter section receives base band signals and up-converts them to an intermediate frequency of approximately 450 MHz. This is then mixed with local oscillator frequency of approximately 1.35 GHz, such that a difference frequency allows operation in the GSM 850/950 MHz band, and the sum frequency allows operation in the GSM 1800/1900 MHz bands. The frequency addition allows operation in the UMTS band. The receiver portion of the transceiver comprises a direct conversion receiver for down-converting the received signal without use of an intermediate frequency.