Shortly I was looking for a frame generator where I can put in a screenshot from iPhone or iPad and then automatically a screenshot with the device's frame is created.
Something identically has already been existing for Android for a longer time, for iOS I needed to dig a little bit deeper, however after a couple of blog and stackoverflow postings I discovered two nice solutions for Apple and one that is already popular for Android.
The first solution for a Apple frame generator can be found directly on the Apple developer site, however the integration of the screenshot needs to be done with Photoshop. The second solution is straight forward and is not for Apple only, it is a Android frame generator too.
For Android device's only a frame generator can be found on the Android Asset Studio homepage a really nice place for discovering cool tools. A look onto this page is really worth seeing.