If you’re not sure what to do with your old iPhone this video might give you an idea. If not, I suggest jailbreaking it and keeping it around. You should be able to run an unlock process and use it as an iPod Touch with a camera, speaker and microphone and run off of Wifi. I’m going to try and use it along with my new iPhone 3G. I’ve already unlocked my current iPhone so all I have to do is swap in my new SIM from my iPhone 3G and I can use my old iPhone on the network. This way I can have a backup if my battery dies and use all the great Installer apps until the iPhone 3G is jailbroke. We know this works now because both of our iPhones are unlocked and we can swap SIMs and the phones work (using the other phone number of course). Let me know in the comments what your plans are for your old iPhone if you’re upgrading.