If you don’t already know how to add a bookmark to your home screen, simply tap the Menu button in Safari and select the “Add to Home Screen” option, you’ll be prompted to edit the name of the bookmark and just like that you’ve got quick access to whatever websites you want right from your iPhone or iPod home screen.
Of course we’re not done there.
The easiest way to save this bookmarklet onto your iDevice is to actually use your iPhone or iPod, click the link above and follow the instructions in the new window. Once you've save the bookmarklet and labelled it "Set Home Screen Icon" you're ready to move on to the next step.
Now, you’ll need to locate the picture you want to use as the actual thumbnail icon. Just do a Google image search and you shouldn’t have any trouble finding whatever picture you have in mind. Copy the URL for this image.
Now, go to the webpage that you want to set a home screen bookmark for. Then, go to your bookmarks list and click on your “Set Home Screen Icon” bookmark. You’ll be prompted to enter a URL.
Paste the picture URL that you have copied into your clipboard.
Press "Okay." Next, hit the menu button and select “Add to Home Screen.”
There, you’re done. You should have a nice home screen bookmark with the icon you selected. Notice the TSN Mobile bookmark on the left without a custom icon thumbnail versus the icon on the right with the custom thumbnail picture we chose.
Please feel free to use the comments section if you have any questions or suggestions.
Check out this article for more information on the subject.