How can I use an MT5600SMI to transmit the 1300 Hz Calling Tone every time an outgiong call is initiated with the ATD command? Something like the ^M command but it should be stored as a permanent modem setting not only a per-session command.

Unfortunately, the only possible method for turning Calling Tones on for the MT5600SMI is by placing the ^ in the dialing string. There is not a way to store this configuration into the modem.

However, the MT5634SMI series socket modems do support this. The ATS35=1 turns on calling tones and you can store that command to memory with the AT&W command.