This is a custom attachment I designed to clip onto the side of my office phone.
It was basically designed to hold a "cheat sheet" of select internal phone numbers for commonly called colleagues. I personally find it easier to hit the "transfer" button and type in the three digit short code than press the address book button and start searching through names/numbers whilst I know someone is effectively waiting on hold.
Still a work in progress, trying to find a secure way to clip the front and back parts together.
Update: 5th version in the iterative design. Thinned out edges for quicker print as well as larger frame for extra information in the "cheat sheet". clip mechanism added to front and back of frame so they "snap" together nicely. Also, clip brackets shortened and angled for better viewing when phone is laying down or standing up.