This looks absolutely awesome. I really need to connect to a Honeywell UDC3500 using Modbus TCP. Do you know of any GPRS modem that we could use which will act as a Modbus Master and be suited to your program? We want to connect to the Honeywell 3500 using dial up mobile phone services for supervisory control. It would also be handy (if possible) for scheduled reporting to be sent to your program as well.
The ScadaMobile or Modbus Gem apps can not act as Modbus Slaves, they are Modbus Masters. You should be able to use any GPRS Router to connect remotely to your controller. You only need to configure the usual port forwarding setup on your Router to allow it to forward TCP packets to your Controller. The Modbus Slave is then your Controller, and the ScadaMobile app acts as a Modbus Master connecting to your Controller through the Internet IP of the GPRS router.