If you change your mind about turning the iPhone off, tap the Cancel button, or do nothing. If the iPhone decides that you’re not paying attention, it dismisses the “slide to power off” screen automatically.

The iPhone can demand a password each time it wakes up, if you like.

You can’t use any other company’s SIM card in the iPhone – it’s not an “unlocked” GSM phone (at least, not officially; there are some unauthorized ways). Other recent AT&T cards work, but only after you first activate them. Insert the other card – it fits only one way, with the AT&T logo facing up – then connect the iPhone to your computer and let the iTunes software walk you through the process.

Geeks may enjoy knowing that the screen is 320 by 480 pixels.

On the iPhone 3G, you can use any standard headphones with the iPhone – a welcome bit of news for audiophiles who don’t think the included earbuds do their music justice. But on the original iPhone, the molding around the iPhone’s audio jack prevents most miniplugs from going all the way. You must be able to get your headphones to fit by trimming the plastic collar with a razor blade – or you can spend $10 for a headphone adapter (from Belkin.com, among others) to get around this problem.

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