In order to simplify the setup of telephone conference with distributed conference devices, each conference participant applies speech encoding to its own speech signal in order to reduce the bandwidth of its speech signal thus that the bandwidth compressed speech signal shows at least half of the bandwidth of the data transport channel. Each compressed speech signal is inserted to the data transport channel and that each conference participant extracts the compressed speech signals of the other parties from the data transport channel. Each participant then decodes the compressed speech signals and each conference participant sums up all decoded speech signals to a sum signal.