Despite the iPhone's entirely touchscreen-driven interface, all of its external buttons are mechanical and have a distinct, clicky tactility. There is, of course, the home button on the face, which takes you back to the main menu; along the left side of the unit is the volume up / down rocker (which is clearly identifiable by touch), and a ringer on / off switch -- something we wish all cellphones had, but that far too few actually do. Turning off the ringer briefly vibrates the device to let the user know rings are off; it's worth noting that turning the ringer off doesn't turn off all device audio, so if you hit play on a song in iPod mode, audio will still come out the speaker if you don't have headphones inserted.
On the top of the unit is the SIM tray (each unit comes pre-packaged with an AT&T SIM already inserted), which pops out by depressing an internal switch with a paperclip. Finally, the largest perimeter button is the sleep / wake switch, which does as you'd imagine. Press it (and swipe the screen) to wake up the device, or press it to put it to sleep; hold it (and swipe the screen) down to shut it off completely. (You can also use it turn off the ringer - -one click -- or shunt a call to voicemail -- two clicks -- if someone rings you.)
