A call-to-listen number (CTL) is a regular phone number that is assigned to a radio station. The number is connected to the station's live stream. The station's listeners can call on the number assigned and listen to that station.
The call is registered as a regular phone call. People are not charged if they have unlimited plans. It works very well in America and other similar countries with unlimited calling plans. Calls use mobile minutes.
Please note it is not a toll-free number.