reformatting phone nubmer

How can I reformat phone numbers to contain dashes,
ex: 123-456-7890. I want the dashes to be added once the user leaves the field.

I imagine tha all the phone numbers in your country have the same length. If so you can do this:

imagine you have number here: form1.phone.value


number = form1.phone.value;
new = number.subtring(0,3)+"-"+number.subtring(4,6)+"-"+number.subtring(7,9);


I think that's it. You have cut the phone number in three parts with dashes inside.

What a mess!!!
I've forgotten the "s" of substring. Try with this one.

new = number.substring(0,3)+"-"+number.substring(4,6)+"-"+number.substring(7,9);

So far, this is what I have

<script language="JavaScript">
function number(field)
{
return (reformat(field , "",3, "-",3, "-",4))
}
</script>


<form name="form" >
<tr>
<td>Phone:</td>
<td><input type="text" name="phone" value="" maxlength=12 onChange="number(this)"></td>
</form>

What do I need to do to get this to work? Adding dashes once the user leaves the field.

function formatPhone(phone) {
return phone.toString().replace(/\D/g,'').replace(/(\d{3})(\d{3})(\d{4})/, '$1-$2-$3');
}

something like that should work.