The document shows how Apple plans on using a magnetic process instead of a mechanical one. The problem with the current SIM tray is that requires an opening in the phone which leaves a way for dirt and dust to enter the phone.
Apple can make the SIM tray lighter than it is currently is with the use of magnets. The Cupertino based tech titan has replaced mechanical fasteners before in the design of the Apple iPad Smart Cover. And in its USPTO application, Apple gives a number of use cases for the design including belts and accessories, watches, headsets and necklaces to name a few.
source: Freepatentsonline via AppleInsider