How to Speed Up the iPhone
A lag in your iPhone's speed is often caused by either several application running in the background, or due to a low wireless signal that causes a lag in data speed. Application multi-tasking is a new feature, as of 2010, of the device that keeps previously opened applications opened while in a different app, but decreases performance speed when several apps are open at once. If it's a performance problem due to a lack of a signal, the Wi-Fi feature bypasses the cellular network and instead connects your iPhone to a wireless network.
Double-tap the "Home" button on the iPhone.
Press your finger against the first application icon in the sub-menu until it jiggles.
Tap the "-" on the icon to close the application.
Push the "Home" button to close out of the sub-menu.
Touch "Settings" on the home screen and touch "Wi-Fi."
Touch the "OFF" tab to enable Wi-Fi, and touch the name of your network.
Type the network's password using the on-screen keyboard, and touch "Join."