Автор: http://www.swissdelphicenter.ch

implementation

 {$R *.DFM}

 function tapiRequestMakeCall(DestAddress, AppName,
   CalledParty, Comment: PChar): Longint; stdcall; external 'TAPI32.DLL';

 procedure TForm1.Button1Click(Sender: TObject);
 var
   PhoneNumber, AppName: array[0..255] of Char;
 begin
   PhoneNumber := '1234567890';
   StrPCopy(AppName, Application.Title);
   tapiRequestMakeCall(PhoneNumber, AppName, '', '');
 end;