A communication system, upon receiving an instruction to transfer deferrable data, determines whether an air interface is congested and, when the air interface is congested, defers a transfer of the deferrable data or transfers the deferrable, lower priority data as higher priority data. When, during a transfer of deferrable data, the system determines that the air interface is congested, the system may terminate the call and save a state of a partially completed deferred data transfer. Subsequent to the termination of the call, the system establishes another data connection over the air interface and transfers any remaining, not yet transferred deferrable data. In order to discourage subscribers from transferring higher priority data as lower priority data, the system may further restrict a transfer of lower priority data to designated time periods while allowing a transfer of higher priority data during the designated time periods and other time periods.