Yes, you can use tel://phonenumber to dial using the browser, but it does not allow you to set it as a speed dial webclip, which is what makes this hack so cool. If you put in only the tel:// url and press Cancel, the browser reverts to the previous url. If you press call, the call is placed and you again lose the opportunity to make it a webclip.
but if you use webclips.us it doesnt actually go to the site before it makes the webclip which is what u want. if you were trying to use the method which you described, it would not be beneficial because you wouldnt get a picture with the web clip anyways