function IsValidTel(tel)
{

var ValidChars = "0123456789 ";

var Char;

for (i = 0; i < sText.value.length; i++) 
{ 
Char = tel.value.charAt(i); 
if ((i == 0) && (Char == "-")) // check first character for minus sign
continue;
if (ValidChars.indexOf(Char) == -1) 
{
alert('Please enter numbers only');
tel.focus();
break;
}
}