How to upload custom iphone themes on Apple iphone:

Assuming you already downloaded and installed SummerBoard on your iphone, you can install other free iphone themes using summberboard software as below step
1. connect your iphone to your pc

2. open WINSCP in order to connect thru lan/wifi to your iphone

3. browse to the /private/var/root/Library/SummerBoard/Themes directory

4. extract the iphonethemes.rar files to a temp directory on your hd

5. browse the themes, and choose whatever you like

6. copy themes directories to your iphones /private/var/root/Library/SummerBoard/Themes directory

7. tap the SMBPrefs icon on your iphone, goto Theme, and pick your favorite theme

How to install iphone themes