Here’s a Helpful Tip for iPhone users! If you’re using an iPhone 3GS, an earlier model, or an iPhone 4, and your phone is becoming sluggish, frozen, & not performing at optimal speed, here’s what you should do. You need to do a hard reboot of your iPhone. Press down the Home button and the top Sleep/Wake button simultaneously for 15 seconds until you see the little Apple logo, then let off both buttons. Give it about 2-3 minutes to reboot, and you’re done. Your iPhone will be good to go. I recommend doing this at least once every two weeks.
Here’s a great video tutorial on how to do the iPhone hard reboot.