function IsNumeric(sText) {
   var ValidChars = "0123456789.";
   var IsNumber=true;
   var Char;
 
   for (i = 0; i < sText.length && IsNumber == true; i++) 
      { 
      Char = sText.charAt(i); 
      if (ValidChars.indexOf(Char) == -1) 
         {
         IsNumber = false;
         }
      }
   return IsNumber;
   
   }

function check(form) {
	if (form.telephone.value == "") {
		alert("Please enter your telephone number.")
		form.telephone.focus();
		return;
	}
	if (!IsNumeric(form.telephone.value)) {
		alert("Please enter a valid telephone number.")
		form.telephone.focus();
		return;
	}
	else
	{
		form.submit();
	}
}