Handling AT commands is IMHO not the task of STinG. That would mean your terminal program is already talking directly to the serial interface, and that is not catched by a TCP/IP stack. If you have a linux box running in your private network, you may try looking at tcpser
instead. Alternatively, you have to change your terminal program to use the TCP/IP stack itself, but for that you don't really have to change STinG.