Telephone-based data processing device and communication support system

A communication support system includes a command signal recognition unit (6) which discretely detects a command signal sent by a telephone unit (1) and a command signal sent from a telephone network (4), and determines whether the command signal is from the telephone unit, the command signal from the telephone unit indicating one of a plurality of telephone services of a data processing device (3). A signal transmission inhibition unit (8) inhibits transmission of a signal from the telephone unit to the telephone network. A telephone service processing unit (7) performs a telephone service processing of the data processing device for the telephone service indicated by the command signal from the telephone unit, the telephone service processing unit starting execution of the telephone service processing when the command signal recognition unit determines that the command signal is from the telephone unit.