The command AT+FCLASS=8 or AT#CLS=8 will put the modem in voice mode. Most modems still remain on-hook and respond with OK. Once this command has been accepted, most modems will respond with Data Link Escape (DLE) messages instead of or in addition to normal modem responses. For example, instead of reporting a phone line ringing with the RING message, many modems will instead send the DLE ASCII character, followed by the letter R. The specific set of DLE events reported by each modem is specific to its chipset and documented in its reference guide.
