HTML Link to Dial Telephone Number in Mobile Site

I've tried a few things to create a link which will telephone a given phone number in a mobile site... none of which I can get working!
Just takes me to my 404 page.

It's a button which Im using and then inserting code into the placeholder location.

<a href="wtai://wp/mc;18881235467">1-888-123-4567</a>
and
<a href="tel:5551234567">Call (555)123-4567</a>

Any ideas on a link which will work and dial the number?

tel:

Doh! ;) Thanks GWP