function IsNumeric(phone)

{
   var ValidChars = "0123456789";
   var IsNumber=true;
   var Char;

 
   for (i = 0; i < phone.length && IsNumber == true; i++) 
      { 
      Char = phone.charAt(i); 
      if (ValidChars.indexOf(Char) == -1) 
         {
         IsNumber = false;
         }
      }
   return IsNumber;
}

function checkform(form)
{
  if (form.name.value == "") {
    alert( "Please enter your name." );
    form.name.focus();
    return false ;
  }
  if (form.phone.value == "") {
  	alert( "Please enter your phone number." );
  	form.phone.focus();
  	return false ;
  }
  if (!IsNumeric(form.phone.value)) { 
	alert( "Please enter only numbers in the phone field." ) ;
	form.phone.focus(); 
	return false ;
  }
  if (form.email.value == "") {
    alert( "Please enter your email address." );
    form.email.focus();
    return false ;
  }
  return true ;
}