The idea is originated from the movie The Illusionist. We've just posted our first deisgn of such locket (please see "customized Illusionist Locket for photos" in Shapeways), and this is an updated for containing trinkets, like rings. Based on our optimized geometric algorithms, our locket can maximum the container volume and shapeshift smoothly.
Moreover, we can design your very own one. If you tell me the size/ color/ words/ pattern you like, eg. your lucky number/ favorite color/ names, we will design it for you. Please don't purchase this sample, because it's assembled by 4 parts, not only one. This sample is ONLY a reference.
If you let us design your personal own locket, please contact us at firstname.lastname@example.org. We'll quote for you based on how large your locket is and how much design work you want us to work for you. You can still pay safely through Shapeways when we upload your model. The sample is your price reference.
P.S. If you want other materail, please also contact us because we need estimate if it's 3D-printable. We've tried aluminium and ceremics in different sizes, but not all successful.