This is are some guides on how to obtain free iphone themes onto your iPhone or iPod Touch.
Basically free iphone theme is collections of the icon in .png format that load into your Homescreen. What is Homescreen? Homescreen is where your User Interface which is contains many of icons displayed on your device. It may includes App, Games or Tools and many more.

So the iphone theme will transform these icons and change your theme. It can be activated via Winterboard, which is controls your UI or Icons on Homescreen. Other than iphone themes, Winterboard also can transform lockscreen, icons, volume icon, battery icon,wallpapers.
lockscreen sound, fonts and many more. You can get Winterboard from Cydia. However that, don't forget to jailbreak your iPhone or iPod Touch first.

So how to download iPhone themes to your iPhone? It is very easy. Just follow through my guides.

Firstly you need to jailbreak your iPhone 1G devices. It can be done using jailbreak tools such as blackra1n, l1merain,spirit jailbreak and many more. After that, you need to download Free Phone Wallpapers HD iPhone themes from the website that provides free iPhone themes.
There is one website that I know you can get the free iPhone themes easily. The URL is

Select your desired free iPhone theme and then download it into your personal computer. Then you will get .zip files. You must extract the .zip files into somewhere in you PC.

Now what you need to do is, you need to SSH or connect your iPhone via USB to your personal computer in order to transfer the iPhone themes into your iPhone 4G. You can use WinSCP if you are Windows user to SSH. If you want to transfer via USB you can try iFunBox software.
After that,you need to locate the themes folder first. Find this folder in the file explorer. All the themes will be posted in Library/Themes. Let say the theme that you have downloaded is named Zune HD.zip. Then extract the Zune HD.zip into one folder name Zune HD.

Then drag and drop the folder into Library/Themes. Easy isn't it ?

After that, plug out USB or SSH. Then open Winterboard inside your devices. You will see one the theme that you uploaded before is now appear in Winterboard app. It is named Zune HD.

To enable or activate the theme, just tick on the theme's name. Then the theme will be enabled.

So let's check what you instructed :
Firstly jailbreak your iPod touch 4G.
Install Winterboard.
Get free iPhone theme from website given above.
Extract the theme that you have downloaded
SSH or connect via USB from your device to your computer
Drag and drop the theme into Library/Themes folder
Activate the theme by using Winterboard app
Finish!

Enjoy your new free iPhone themes