Unable to transfer call using AT Command

I have created a console application that connects to my modem using AT Commands. I am able to dial a number and it works fine.

I want to transfer a call to a different number, and I am unable to achieve this. The modem first dials the number 5052, drops the line and then dials 5056. I am using the hook-flash option that is used to transfer the call but it is not working, instead it is dropping and initiating a new call.

Code:

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SerialPort port = new SerialPort("COM3", 115200);
port.Open();
port.ReadTimeout = 5000;
port.NewLine = "\r";
port.WriteLine("ATZ"); // reset the modem
port.ReadTo("OK\r\n"); // wait for "OK" from modem

port.WriteLine("ATDTW5052@"); // dial number with dialtone
port.WriteLine("ATDT!5056"); // dial number with dialtone

string response = port.ReadTo("\r").Trim(); // read until first newline
Console.WriteLine(response);
//port.Close();

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Does your modem support these "ATDTW" and "ATDT!" commands?
Did you try to send them using HyperTerm?

I have tried ATDTW and it works. The transfer using flash hook doesn't seem to work.

Since ATDTW is working, can i assume that my modem support ATDT! as well?

Is there a way to find out AT commands that are compatible?

Quote:

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Originally Posted by fawadhq

Is there a way to find out AT commands that are compatible?

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Yes, you just have to read the documentation of your modem.

Quote:

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Originally Posted by fawadhq

I have tried ATDTW and it works. The transfer using flash hook doesn't seem to work.

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Did you try ATD! instead?

Yes even tried ATD! and it didn't work.
It drops the first call and then dials the second number.
Where as what i want is to transfer the call.

As far as I understand it that's how it should work. ATDT! cause the modem to go on-hook a short period. See http://michaelgellis.tripod.com/modem.html