Electronic devices may be provided that contain wireless communication circuitry. The wireless communication circuitry may include radio-frequency transceiver circuitry coupled to antennas by switching circuitry. Multiple radio access technologies may be supported. A device may include first and second antennas. Control circuitry can configure the transceiver circuitry and switching circuitry to support operation of the device in active and idle modes for each radio access technology. In some configurations, both antennas may be used to support operations associated with one of the radio access technologies. In other configurations, the first antenna may be used to support operations with a first of the radio access technologies while the second antenna is used to support operations with a second of the radio access technologies.