Disclosed is a method of integrating voice and data services onto a same frequency channel using available transmit power information to determine data rates, wherein the available transmit power information indicates an amount of transmit power available for future data transmissions over one or more data channels. In a “distributed” embodiment, a transmitter or base station transmits, via a forward link, an available power message to a receiver or mobile-telephone indicating an amount of available transmit power at some future time t+z. The mobile-telephone performs signal-to-interference measurements corresponding to the received forward link and received interference, and uses such signal-to-interference measurements and the available power message to determine a data rate that can be supported by the mobile-telephone. Preferably, the determined data rate corresponds to a maximum data rate at which a minimum level of quality of service can be achieved at the mobile-telephone. In a “centralized” embodiment, the mobile-telephone transmits the signal-to-interference measurements to the base station, and the base station determines the data rate based on the available transmit power at future time t+z.