A friend recently lost her iPhone (running iOS 7.1.2). Thankfully, someone found it before the screen turned itself off and go through her list of contacts,, and she got her phone back; Otherwise, the person wouldn't have been able to get into the phone because of the pin number that locks the phone.
I remember that on a Blackberry, it was possible to display an email or phone number on the home screen even when the phone was locked. Can an iPhone running iOS 7 be configured likewise?