To defense your iPhone
Here are some basic and advance defense technique you can use it on your iPhone.
Basic defense
Use a password
Go to Settings>General>Passcode Lock to set your password. Remember to enable the “Erase Data” option, this will wipe out all data on your phone after 10 failed passcode attempts.
Install Anti-theft and snoop detection alarm

This software will cost you US$0.99. It worth buying this software as you do not wish to spend another few hundred bucks to buy another iPhone. This app works based on the iPhone accelerometer. Once it is armed, any movement detected by the accelerometer will be interpreted as an attempt to swipe your iPhone. Then an alarm will sound off.
Install Motion Alarm

Price at US$1.99 and is available at crowdedroad.com. This app is similar to the previous software just that it is more sensitive and if set to stealth mode option it allows the app to secretly send its GPS coordinates to a preset e-mail address.
Advance defense
Install MobileMe

Not sure about this pricing but by looking at the features it provide, it definitely going to be expensive. Once the program is install in your iPhone you can go to MobileMe site to assign a passcode remotely or set the phone to pop up a message. It is also able to estimate your handset’s location on Google Maps. If your phone is stolen you can choose to remotely wipe out all data on your iPhone. Moreover the only way to disable MobileMe features is to do a hard reset.
via digital life