Locking down all apps except the phone/call app on the iPhone 4 running iOS6? Is there a way to lock out all apps except just the phone app in order to make calls?

I understand "Guided Access" isolates you to a particular app and not let you move out. 
This works fine but is annoying as you cannot lock the phone (in other words "The hardware buttons are always off") when its on. Is there a way for me to enable just the lock button?

Please advise.
You can turn on Restrictions in iOS Settings (in the General section), which allows you to disable all non-standard apps, as well as some of the built-in ones (such as Safari, Camera, FaceTime, iTunes and Siri). Unfortunately, I believe a few built-in apps remain, such as Messages, Calendar and Maps, I'm not aware of a way to disable them completely.

A word of caution if you're testing this out—disabling apps, then re-enabling them will destroy your home screen organization.