This thread discusses about sending SMS from the S7 - 1200 to a Teltonika device, however, apparently, most of the configuration is performed on the PLC side, which I am unfamiliar with, but there seems to be enough information and reference links to get the idea.
From what I managed to find, to access the TIA portal remotely, your TRB140 would need to have a public IP and its LAN IP configured as a gateway.
Best regards,