Apple has limited the number of home screens on the iPhone to 11. Even though that adds up to a total of 180 applications including the dock, some users want more space. This is possible on firmware version 3.1.2 thanks to a trick that doesn't require jailbreaking.
Follow these steps to get more than 11 home pages on your iPhone:
1. Make sure you have 11 pages of apps. You can drag apps over to create a new page.
2. Blank spaces are OK, but the first and last page must be completely full of apps (16 on each).
3. Move the Voice Memos icon to the last position on the last page (all the way in the bottom right, but not in the dock).
4. While the icons are still wiggling, move one icon up from the dock to bump the Voice Memos icon off the screen and replace it in the last position.
5. Press the home button so the icons stop wiggling and reboot the iPhone.
6. You now have 12 home screens. Just readjust the icon positions how you like them and return the icon you moved from the dock back to the dock.
7. Repeat the process for more pages.
As the Apple iPhone School brings to our attention, 19 pages will give you 19 grey dots, the maximum that will fit at the bottom of the home screen.
Warning! Syncing your iPhone with iTunes 9.0.2 will return your iPhone to 11 home screens.