I have the iPhone, and I’d like to have the functionality to password protect certain applications on it, such as SMS/Text and Mail. It’s just something about me, because sometimes people borrow my phone, and I don’t feel comfortable having my personal information seen and read.

Well if you have a jailbroken phone with the Cydia application, then you’re in luck. There’s an application called “Lockdown” that allows you to put a password on any application that you want — and that includes applications such as Photos, Mail, and SMS 🙂
thanks! good recommendation
man this Password Protect Sensitive Applications (SMS, Mail) on the iPhone is hot.
I got Iphone 3Gs and its running on iSO 4.0.1 (jailbroken) tried lockdown but it doesn't run with 4.0 iSO… any other apps new or old which are compatible with the new software?
I'm not sure about ios4, a lot of apps broke with that update. and i switched to android, so I didn't keep up 😀