Оформил: DeeCo
Автор: http://www.swissdelphicenter.ch

uses
   WinInet;

 // Causes the modem to automatically dial the default Internet connection. 
procedure TForm1.Button1Click(Sender: TObject);
 var
   dwConnectionTypes: DWORD;
 begin
   dwConnectionTypes := INTERNET_CONNECTION_MODEM + INTERNET_CONNECTION_LAN +
     INTERNET_CONNECTION_PROXY;
   if not InternetGetConnectedState(@dwConnectionTypes, 0) then
     // not connected 
    if not InternetAutodial(INTERNET_AUTODIAL_FORCE_ONLINE or
       INTERNET_AUTODIAL_FORCE_UNATTENDED, 0) then
     begin
       // error 
    end;
 end;


 // hangup the default Internet connection. 
procedure TForm1.Button2Click(Sender: TObject);
 var
   dwConnectionTypes: DWORD;
 begin
   dwConnectionTypes := INTERNET_CONNECTION_MODEM + INTERNET_CONNECTION_LAN +
     INTERNET_CONNECTION_PROXY;
   if InternetGetConnectedState(@dwConnectionTypes, 0) then
     // connected 
    InternetAutodialHangup(0);
 end;