How to Password Protect Applications on iPhone
LockDown
Unfortunately, even in iPhone 3GS, we can only set a passcode to gain access to iPhone’s home screen but we don’t have App-Specific password protection. I don’t mind passing my phone around at a party to share a YouTube video or funny web site, but you have to keep a close eye on people to make sure they don’t go messing around with things they shouldn’t be. Like I don’t want others to have access to Email App or SMS or Photos.
Once again Thanxs to the Jailbreak Community where iPhone users can enjoy the App-Specific password protection. A free iPhone App: LockDown, available in Cydia has the ability to Password protect your desired application on iPhone. LockDown works like a charm on iPhone OS 3.0 and also supports 2.x firmwares as well.