GigaOm today reported that Apple may be working to embed a custom, writable SIM chip for its next iPhone. This new SIM module would enable Apple to sell its iPhone directly to the market and without the carrier getting involved. It was also reported that SIM card manufacturer Gemalto was working with Apple to create a custom SIM chip that would be embedded in the iPhone.
The SIM card can be reconfigured to work with a different carrier by simply uploading a small file with carrier specific data. These files can be uploaded via a dock connector or by the carrier themselves. If this system is in place, expect to see Apple selling their iPhones directly to you rather than having it to be ordered via AT&T. It will also allow you to simply switch your carrier without having to worry about dumping your phone.
Many European carriers had asked Apple to work on something similar due to high competition between multiple carriers and to give users a more easier way to switch between their providers.