Hi guys,

For those using 3.0, here's a temporary solution.

(Need SSH, if you dont know what that means, stay away from this tutorial)

1. First of all, open Maps and let some tiles load.
2. SSH to your phone, open /private/var/mobile/Libary/Caches/MapTiles/
3. If you do not see the MapTiles folder or MapTiles.db inside it, try doing the first step again.
4. Download any of the rar packages found in the first page of this thread, unrar, and find for the MapTiles.db inside.
5. Replace the MapTiles.db file inside the folder you just SSH'ed to.
6. Finally, change permissions of /private/var/mobile/Libary/Caches/MapTiles/ to 555 to ensure the iPhone doesn't modifies the MapTiles.db file or deletes it. (Make sure to do it recursively, which includes the MapTiles.db file itself).

Personally tested and working. No offlinemaps application required.

Use sbsettings to disable your GPRS.. the maps application will still try to use an active connection to load tiles, but if it doesnt sees a connection, it will load from the file.