com port, telephone line

[bros]

I wrote a program to send same text through the phone line, is OK. But when I need to detect the receiving from the phone line, I can't detect it.
e.g. When I made a call to my friend, when he start talking, I like to detect the voice (first chr) symbol, then I can auto send some data to him. Just like the SUPERVOICE can detect the fax coming and received the fax. Can I know the data bit sysmbol?????

 

[Foada]

Can you post some code? Anything is possible, the problem is I only have one lifetime.