Save images in safari and mail
Just touch and hold an image in Safari or Mail, an action sheet will be presented to enable you to save the image. The image will get stored in the "Saved Photos" library of the Photos app.
Access iPod controls or phone favorites instantly
Go to "Settings -> General -> Home Button". Double taping the home button goes to "Home", "Phone Favorites" or "iPod Controls".
Forward/rewind music & video
Press and hold the skip forward/back arrows to fast forward or rewind rather than skip tracks. Also, press on the album art to manually FF/rewind.
Use iPhone as a Modem
You can use iPhone 3G or later as a modem to connect, or tether, your computer to the Internet. You can connect iPhone to your computer using the Dock Connector to USB Cable, or via Bluetooth.
In Settings, choose "General -> Network -> Internet Tethering".
Slide the Internet Tethering switch to On.
Connect iPhone to your computer:
USB: Connect your computer to iPhone, using the Dock Connector to USB Cable. In your computer’s Network services settings, choose iPhone. On a Mac, a pop-up window appears the first time you connect, saying "A new network interface has been detected". Click Network Preferences, configure the network settings for iPhone, then click Apply. On a PC, use the Network Control Panel to configure the iPhone connection.
Bluetooth: On iPhone, choose "Settings -> General -> Bluetooth" and turn on Bluetooth. Then refer to the documentation that came with your computer system software to pair and connect iPhone with your computer. When you’re connected, a blue band appears at the top of the screen. Tethering remains on when you connect with USB, even when you aren’t actively using the Internet connection.
Monitor your cellular data network usage: In Settings, choose "General -> Usage".
Earbud Cord Switch
Without close inspection, you’d have a hard time telling the iPhone’s white stereo earbuds apart from a regular iPod’s-but don’t get them mixed up. The iPhone’s earbuds have a tiny, embedded clicker/microphone partway down the right earbud cord.
That’s right, "Clicker/Microphone". The tiny bulge is the microphone for phone calls. But if you pinch the bulge, you’ll find that it clicks.
Pinch once to answer an incoming phone call. Pinch twice to dump the call to voicemail. (You can also tap or double-tap the "Sleep/Wake" switch on top of the iPhone for the same functions.)
During music or video playback, pinch once to pause the music; pinch again to resume playback. During music playback, double-pinch to skip to the next song.