Hello Daniel,
There are two problems I see here. The first one is that if you have a PCI modem, since that is not an NI hardware, you will have to create a driver for RT for that hardware. Other solution is to use a serial board and then talk to an external modem through serial.
Now the second problem that I see here is that you are talking about sending a text message to a Windows application. You must remember that the RT side of the DAQ board is mainly for data acquisition. You would need to have RT on the computer where you will have the PCI board, because the PCI RT will not know that there is a modem next to it and it will not have the drivers for it. And even if it had them, the modem would have to be a daughter board for this PCI RT board.
That is why it would be better to have RT in the computer, not in a DAQ board. And once in the computer, you can work with the serial, TCP or whatever you might need.
Now, once you get the messages, definitely there should be many ways to work with the data before transmitting or receiving, but first we need to define the architecture.
Ricardo S.
National Instruments.