Note: In order to do this you need to be Jailbroken and know how to SSH, learn how to do that Here!
Now you need to install Winterboard to easily change themes. just open cydia, search for winterboard, and install. The "springboard" is that thing on your phone where all your icons are, the main UI basically. This enables you to Theme. You just open the Winterboard app after install and toggle what you want. In order to use themes, just download them to your hard drive and SSH them into your phone.
you click on the ".." at the top of the folder list on the right screen in WinSCP to go back one directory, it defaults to "root" After you go back one directory you will see some folders. open "stash" then "themes" now this is where you store your downloaded theme folders, just stick them in here.
Now you can open Winterboard app and select the theme you want to use. When you hit the Home key, it will respring automatically for you (could take a min) and re-load with your new theme intact.
now just enjoy it or modify it with the included instructions. Take a look at this forum for some awesome themes.
for the more complicated UI changing themes you will have to download and use some more components, such as "Categories" (from cydia) and "IBlank". I would recommend you install both of these from Cydia right now.
To add your custom ringer!
Another slam on the iphone is that you can't set MP3s as ringtones, and it is harder than $%&^ to just put your own music as a ring tone. This is true, thanks apple. Here's how I do it, if you know if a better way reply in this thread and I will edit this post.
1) download Iringer http://www.iringer.net/
(bottom of the page)
2) open Iringer.
3) click "import" and import your MP3 (yes I know the ads are annoying but it's sorta free)
4) click export (if you try to export to scp it say you have to pay $, not to worry you can manually SSH it)
note: it will only export the first 30 seconds, as the iphone cannot support a longer ringtone.
5) open My Documents > Iphone Ringtones and find your file ****.m4r
6) SSH into your iphone (see above) and double click the .. to get out of root (go to an earlier directory) and go to stash
, find the ringtones
folder, open it and move your new m4r there.
7) you're good to go, now you have your custom ringtone. Let me know if this does not work or confusing