I am not a big fan of these types of applications, and generally I wouldn't post it. Although, I have been reading a lot about how people's significant others (girlfriends, and wives) are trying to monitor their mate's electronic communications (SMS, Email, etc.).
iTrust advertises itself as a "keylogger" for the iPhone or iPod touch. While its not by any means a true keylogger, it can tell you if someone was messing with your iPhone. Also I am pretty sure if they push the Home button on the phone this app will be disabled instantly.