I recently upgraded from a 1st gen 8 GB iPhone to a 16 GB 3G 2nd gen iPhone. The 3G iPhone does not come with a dock, unlike it’s predecessor, and the Apple Store was out of docks when I purchased the phone.
I discovered that the new iPhone is slightly wider and a little deeper in the middle than the old iPhone. Rather than pulling out another $30 and ordering a new Dock online, I pulled out the old Dremel instead.
It took about 5 minutes. You have to grind out a little bit of plastic in the middle of the back of the slot to accommodate the thicker in the center iPhone. You also have to grind out the sides, expanding the width of the slot a bit. Then the new iPhone fits easily and solidly in your old dock. If you use a fine grit grinding accessory and a high speed Dremel you can’t even tell that the dock has been modified.
So if you have a Dremel, save yourself $30.