TCall
myCall=MyAddress.CreateCall("0",LINEADDRESSTYPES.PhoneNumber,TAPIMEDIATYPES .AUDIO)
TTerminal t=myCall.RequestTerminal(TTerminal.FilePlaybackTerminal,
TAPIMEDIATYPES.AUDIO, TERMINAL_DIRECTION.TD_RENDER)

in this code TTerminal object always returns null.

Before that I tried using Tapi3Lib directly;

         ITAddress oAddress;      
         ITMediaSupport ims = (ITMediaSupport)oAddress;
         ITTerminalSupport its = (ITTerminalSupport)ims;  //Error

When I try to crate ITTerminalSupport I get "unable to assign... Such an
interface isn't supported" error.

I'm using Agere Systems HDA modem. As I said I got no problem calling. Is
the problem about my modem's audio support? I also tried the codes on a few
laptops and I got same errors.

private void btnPlay_Click(object sender, EventArgs e)
        {
            Object[] playList = { "C:\\myfile.wav" };
            ITTerminal PLyTerminal=
bcc.RequestTerminal(TAPI3Lib.TapiConstants.CLSID_String_FilePlaybackTermina l,
TapiConstants.TAPIMEDIATYPE_MULTITRACK, TERMINAL_DIRECTION.TD_CAPTURE);
            ITMediaPlayback MediaPlay=(ITMediaPlayback)PLyTerminal;
            MediaPlay.PlayList = playList;
            ITMediaControl MediaControl = (ITMediaControl)MediaPlay;
            bcc.SelectTerminalOnCall(PLyTerminal);
            MediaControl.Start();
        }

and use below code for dial:
private void btnCall_Click(object sender, EventArgs e)
        {
           bcc = (ITBasicCallControl2)ln.CreateCall(textBox1.Text,
TapiConstants.LINEADDRESSTYPE_PHONENUMBER, TapiConstants.TAPIMEDIATYPE_AUDIO);

            bcc.Connect(false);
            }

And For Andreas's question. How can I understand if a modem supports voice