To provide a communication terminal that can maximally avoid faults when there are faults in a control program for communication, a server that provides the communication terminal with information on fault avoidance, and a communication system and a communication control method using them.

An upgrade processing part 215 of a cellular phone 206 appropriately applies a correction program for correcting faults to a communication processing part 214 connectable to a plurality of different communication networks. A server sending processing part 218 sends version information about the correction program in the associated device to the information server storing communication mode information representing communication modes using communication networks suitable for respective correction program versions, to inquire corresponding communication mode information. A server reception processing part 219 sets the communication mode according to the inquiry result to cause the communication processing part 214 to use only the corresponding communication network.

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