Data communication method, data communication system, and communication terminal

A portable telephone unit 10 receives management information comprising size information for contents data wanting to be downloaded, and adjusts an environment for receiving the object data, based on size information for contents data contained in the management information. To adjust the environment for receiving the object data it is possible, for example, to determine a communication system for receipt, or to secure a storage region for storing object data that has been received. After that, the portable telephone unit 10 transmits a contents data download request, and receives contents data returned in response to the download request. As a result, it is possible for the communication terminal to download the contents data in a state where the receive environment has been optimized according to the size of the contents.