My favorite iPhone utility (
Iphone PC Suite) works with jailbroken v1 iPhones with the 2.0 firmware installed. If you don't know what this is, it has a pretty slick interface that enables disc access to the iPhone. You can also back up your iPhone with it. And it has sections for summerboard themes, custom ringtones, wallpapers, etc. I'm not sure if the summerboard themes work yet though. I'll check in a while.
EDIT: Sadly summerboard themes don't work. In fact not much really does work. Right now it's mainly useful for backing up your iPhone.
After you jailbreak your v1 iPhone, hook it up to your computer and start PC Suite. It will tell you that you don't have some daemon tools installed on your iPhone. After you press the install button it will ask you to restart your iPhone, press a button, then restart your iPhone once more, then press another button. When I did this, it told me that it failed. But it really didn't fail. Now iPhone PC Suite can connect to my iPhone and I can backup my Voicenote sound files.
*iPhone PC Suite might even work with the 3G but I don't know. Maybe someone with a 3G can confirm that it works.
**Obviously I take no responsibility for any harm that happens to your iPhone should anything go wrong. Perhaps it will brick your phone, but mine was fine.