This is a speed dial trick that has covered before, however I still think it is pretty cool, till a native app appears. Thanks to Nate at Cre.ations.net for discovering and coming out with an effectively way to use this feature, Jeff Carroll for creating some improvements such as Base64 encoding and the Zeigen for creating a nice front end for it.
The trick is basically a javascript written to input the phone number and image you want to create a speed dial on your iPhone home screen. Mobile Safari since firmware 1.1.3 has a feature to “Add a Home Screen button” of your favorite sites on your iPhone home screen, thus giving you the ability with one tap to bring up Mobile Safari to the respective saved websites. Now add that feature with the ability to call any number located within a web page that has link to a number, utilizing tel:/number feature, you shall have a speed dial, except it will prompts you to confirm the call upon tapping the button you created.
If you interested you can view the respectively scripts each has written, by clicking on the links below and viewing the source of the page, they have each allowed viewers to review their the scripts and understand how it works. However, if you are concern about the privacy, kindly ask their permission to use the scripts on your own server and do give them credit on the work 
Enjoy!
