Of course, many of you will opt to keep your current iPhone. In that case, here's a list of fun and useful things you can do with the "old" iPhone you once loved so dearly.
Continue to use it as a phone
There are a few ways to use your old iPhone as a phone once it's off a formal plan. For one, you can install Skype (or one of the many VoIP apps) for Wi-Fi based voice over IP calls. There are a few caveats to keep in mind with Skype, however. In order for the iPhone to maintain a Wi-Fi connection, the iPhone can't go to sleep, so keep it connected to a power source. Also, a call coming in via Skype won't ring, only vibrate. So take the case off and put it on a cookie sheet and let it rattle around like a coffee can full of bb's when a call comes in.
Alternatively, if you're the jailbreaking type, get yourself a H2O prepaid SIM card from Best Buy.
Keep reading for more fun ideas.