A data communication transceiver, such as a PCM or xDSL modem, is operable in a training-while-working mode in which it both trains and communicates user data. In some embodiments, upon initiation of a data communication session, the transceiver operates in a startup training mode in which partial training occurs that is sufficient to enable low rate data communication; the transceiver then enters the training-while-working mode in which it communicates user data and completes training. When training is completed, the transceiver enters a data mode in which it communicates user data but does not train. In some embodiments, if in the data mode conditions arise requiring retraining or making retraining desirable, the transceiver enters the training-while-working mode and retrains while continuing to communicate user data.