Screen Icons

Here's a roundup of the icons that you may see in the status bar at the top of the iPhone screen, from left to right.

Cell Signal. As on any cellphone, the number of bars indicates the strength of your cell signal, and thus the quality of your call audio and likelihood of losing the connection. If there are zero bars, the dreaded words "No service" appear here.
EDGE Network. When this logo appears, your iPhone can get onto the Internet via AT&T's very handy, but very slow, EDGE cellular network (A Tale of Two Networks). In general, if you have a cell signal, you also have an EDGE signal.
Airplane Mode. If you see the airplane instead of signal and Wi-Fi bars, the iPhone is in Airplane mode (Turning Off the Antennas—and Airplane Mode).
Wi-Fi Signal. When you're connected to a wireless Wi-Fi Internet hot spot (A Tale of Two Networks), this indicator appears. The more "soundwaves," the stronger the signal.
The iPhone is locked—meaning that the screen and most buttons don't work, to avoid accidental presses—whenever it goes to sleep. In Locked Mode.
2:34 PM. When the iPhone is unlocked, a digital clock replaces the Lock symbol. To set the clock, General.
Play indicator. The iPhone's playing music. Before you respond, "well, duh!," keep in mind that you may not be able to hear the music playing. For example, maybe the earbuds are plugged into the iPhone but aren't in your ears. So this icon is actually a handy reminder that you're running your battery down unnecessarily.
Alarm. You've got an alarm set. This reminder, too, can be valuable, especially when you intend to sleep late and don't want an alarm to go off. General for setting (and turning off) alarms.
Bluetooth connection. The iPhone is connected wirelessly to a Bluetooth earpiece or hands-free car system, as described Alarm. (If this symbol is gray, it means that Bluetooth is turned on—and draining your battery—but it's not connected to any other gear.)
TTY symbol. You've turned on Teletype mode, meaning that the iPhone can communicate with a Teletype machine. (That's a special machine that lets deaf people make phone calls by typing and reading text. It hooks up to the iPhone with a special cable that Apple sells from its Web site.)
Battery meter. When the iPhone is plugged into its cradle (which is itself plugged into a wall outlet or computer), the lightning bolt appears, indicating that the phone is charging. Otherwise, the battery logo "empties out" from right to left to indicate how much charge remains.