Advanced group services for use in a mobile phone network include a prepaid billing solution. In the mobile phone network, a real-time exchange interfaces to at least one mobile switching center to provide the advanced group services therein. Both the real-time exchange and the mobile phones that use the advanced group services communicate with each other using call setup and in-band signaling within the mobile phone network, wherein the real-time exchange switches the voice frames for the advanced group services between the mobile phones across bearer paths and through at least one mobile switching center in the mobile phone network. A real-time billing mechanism is provided for a prepaid subscriber of the advanced group services. The real-time billing mechanism may use a prefix-based billing solution or a charging number based billing solution.