Patent ID: 7194074

Claim:
A key telephone system comprising: a key telephone; and a main unit which inquires of said key telephone about a transmission scheme, and determines a data transmission scheme between said main unit and said key telephone on the basis of a reply, the main unit comprises: a communication section configured to communicate data with the key telephone by either of first and second transmission schemes; a model determination section configured to determine whether the key telephone is compatible with both of the first and second transmission schemes or only the first transmission scheme; a selection section configured to select the first transmission scheme when the key telephone is compatible with only the first transmission scheme, and select the second transmission scheme when the key telephone is compatible to both of the first and second transmission schemes; a transmitter configured to transmit a mode inquiry to the key telephone by the first transmission scheme; and a mode controller configured to change the transmission scheme to the second transmission scheme upon reception of a response from the key telephone.