function agregar_codigo_tel(){
  var pais = document.getElementById("combo_pais");
  var num="";

  switch(pais.value){
     case "DE": num=49; break;
     case "AR": num=54; break;
     case "AU": num=61; break;
     case "AT": num=43; break;
     case "AR": num=54; break; 
     case "BE": num=32; break;
     case "BR": num=55; break;
     case "BG": num=359; break;
     case "CA": num=1; break;
     case "CL": num=56; break;
     case "CN": num=86; break;
     case "AR": num=54; break;
     case "CO": num=57; break;
     case "KR": num=82; break;
     case "DK": num=45; break;
     case "ES": num=34; break;
     case "US": num=1; break;
     case "EE": num=372; break;
     case "FI": num=358; break;
     case "FR": num=33; break;
     case "GR": num=30; break;
     case "HU": num=36; break;
     case "IE": num=353; break;
     case "IL": num=972; break; 
     case "IT": num=39; break; 
     case "JP": num=81; break; 
     case "LI": num=423; break; 
     case "LU": num=352; break; 
     case "MY": num=60; break; 
     case "MX": num=52; break; 
     case "MC": num=377; break; 
     case "NO": num=47; break; 
     case "NZ": num=64; break; 
     case "NL": num=31; break; 
     case "PE": num=51; break;
     case "PL": num=48; break;
     case "PT": num=351; break;
     case "PR": num=1787; break;
     case "UK": num=44; break;
     case "CZ": num=420; break;
     case "RU": num=7; break;
     case "SG": num=65; break;
     case "SE": num=46; break;
     case "CH": num=41; break;
     case "TW": num=886; break;
     case "VE": num=58; break; 
  }
 
  document.getElementById("codigo_pais").innerHTML=pais.value+": ";
  document.getElementById("codigo_tel").value=num;
  document.getElementById("tel").focus();
}