Here's how to do it:
1. Tap settings (from home page)
2. Tap safari, then clear the history, cookies, and cache using the buttons near the bottom of the page.
3. Press the home button.
4. Press and hold both the home and sleep/wake buttons for 10-12 seconds, until the screen flickers off. This will do a "soft reset" on your iphone, just like turning it on and off, but it also empties recently deleted items.
Note: You will
NOT loose any of your prefs or data when doing a soft reset. Also, keep holding down even after you see the "Slide to Power off" screen, and then your iphone will reset a few seconds later.