A modem includes a communicating module, a multimedia terminal adapter (MTA) module, a parsing module, and a selecting module. The communicating module sends a configuration file request packet to a TFTP server to get configuration files including a file ID. The parsing module parses the configuration files to get the file ID. The selecting module configures the MTA module corresponding to the file ID. The communicating module further communicates with a VoIP network according to a protocol corresponding to the file ID.