function checkPhonenumber( form ){
	phonenumber = form.phonenumber.value;
	phonenumber.replace(/-| /g,'');

	if (phonenumber == "") {
    document.getElementById('messageArea').innerHTML = "Geen telefoonnummer ingevuld";
    form.phonenumber.focus();
    return false ;
  } else if (phonenumber.length < 8 || phonenumber.length > 12) {
  	document.getElementById('messageArea').innerHTML = "Ongeldig telefoonnummer ingevuld";
    form.phonenumber.focus();
    return false ;
  } else if (phonenumber.charAt(1) == 8){
  	document.getElementById('messageArea').innerHTML = "Geen servicenummers toegestaan";
    form.phonenumber.focus();
    return false ;
  } else if (phonenumber.charAt(1) == 9){
  	if (phonenumber.substring(2,4) == 91){
  		return true;
  	} else {
  		document.getElementById('messageArea').innerHTML = "Geen servicenummers toegestaan";
    	form.phonenumber.focus();
    	return false ;
    }
  } else if (phonenumber.charAt(0) != '+' && phonenumber.charAt(0) != 0){
  	document.getElementById('messageArea').innerHTML = "Ongeldig telefoonnummer ingevuld";
    form.phonenumber.focus();
    return false ;
  } else {
  	document.getElementById('messageArea').innerHTML = "";
  	window.open('', 'foo', 'width=460,height=360,status=no,resizable=no,scrollbars=no');
  	return true ;
  }
}