Not much I can do about my unactivated iPhone so here are a few things I've figured out while waiting for my iPhone to start working.
1. The SIM number is listed on the box. You'll find both the SIM number (the subscriber identity module or ICCID) and the associated IMEI (the international mobile equipment identity) on the bottom of your iPhone box. They are the bottom-most two barcodes, left and right. The IMEI consists of 15 numbers that uniquely identifies your mobile phone. The SIM number is a 20-digit identity that allows you to access the AT&T network.
2. You can display your SIM and IMEI numbers on the un-activated iPhone. Press the little "i" button on the main screen.
3. Attaching peripherals to the unactivated iPhone's dock connector may produce odd effects. I attached speakers and it offered to put my iPhone in Airplane mode (not a good idea, by the way). TUAW reader Tim O. connected a Kensington Pico FM Transmitter and was able to access the iPod application.
4. You can turn the iPhone off and on--but you probably don't want to. The press the sleep/wake and menu button trick works in terms of turning your iPhone off but it may have unpredictable results. Doing this (under instructions from the AT&T tech) apparently (but not provably) wiped my first SIM card.
5. Tapping the screen keeps it awake before you can adjust those activation-required settings. This is particularly helpful when you're trying to read the ICCID and IMEI numbers off your screen to the AT&T tech.