C#: Problem with communicating via serial port

[grzesiek]

I can't get connection with my mobile phone (modem GPRS)
I write code like this:
SerialPort port = new SerialPort("COM1", 9600, Parity.None, 8, StopBits.One);
port.Open();
port.WriteLine("at");
port.ReadTimeout = 1000;
textBox1.Text = port.ReadLine();
textBox1.Text = port.ReadLine();
textBox1.Text = port.ReadLine();
textBox1.Text = port.ReadLine();
port.Close();
I checked using program portmon.exe that i send commmand "at" but
I havent got any reply. I have error in Visual C# 2005 like this:
The operation has timed out.

[nmsreddi]

hello


i have the same problem ,but i am using GSM modem


any one please help