If you've used a Windows Mobile phone device, you've probably seen the little signal strength icon at the top. If you're lucky, you live in a place with good signal strength and see many bars. If you're like me, you live in a cellular dead spot and are happy when you get one bar.
On many non-WM phones, the part of the icon that's not bars looks something like an antenna--a vertical line with a triangle on top of it. While you sometimes see this antenna icon on WM Phones, it's often something else. And, what that "something else" is varies from device to device. On some it's a G. On others it's an E. On still others it's two arrows pointing left and right. What are these things? What did they do with our beloved antenna triangle? And why won't they go away?
It's all about the data
If your signal strength icon has something instead of an antenna, it means that your device has a network address (an IP address). This means that it can send data to and receive data from the internet. The arrows are our default "data connected" icon. They're often used by CDMA networks for both 1xRTT connections and EvDO connections. OEMs and Mobile Operators have the ability to customize that icon, and often replace the arrows with other things. GSM devices usually have a small "G" or an "E." (Don't confuse these with the larger G or E icon to the left of the signal strength icon. I'll talk more about those later.) The G usually means that you have a GPRS connection and the E usually means you have an EDGE connection. However, some devices can connect to and get faster EDGE speeds but only show the G icon.
Why doesn't it go away?
In our 2002 release, when an application requested a connection to the internet, we'd create a connection. Then, when the application said it was finished with that connection, we'd tear it down. In our 2003 release, we changed this behavior to the current one. Once you've connected once, it stays connected. We made this change for a number of reasons, not the least of which was that it allowed a much better user experience. In 2002, whenever you wanted any data from the Internet, you had to wait a few seconds for the device to request an IP address from the network. Staying connected all the time means that you get data much more quickly. Also, Mobile Operators requested it. It was more expensive for them to be constantly creating and tearing down connections than to just do it once. Finally, staying connected enabled us to develop a fast "push email" client that relied on the device holding an IP address.
It's important to understand that we only do this on connections with "Suspend/Resume" functionality. These kinds of connections are suspended when a phone call comes in and resumed again when it is finished.
Doesn't this cost me money?
In general, no. A long time ago phones sent data over "circuit switched" connections. These were similar to old style modems on your PC. They would make a phone call and send data over that voice connection. The Mobile Operator couldn't really tell the difference between those calls and other voice calls, so they charged per minute. Current data connections (GPRS, etc), though, are different. For these types of connections, every Mobile Operator that I'm aware of now charges per byte transferred, not per minute. So you can keep your data connection on all the time and only get charged when you send or receive over it.
What about my battery life?
Just having a data connection shouldn't affect your battery life. Most of the time, the device isn't doing anything with that connection. It just sits there idle. If you're sending a lot of data over the connection, though, that will definitely impact your battery life. Unfortunately, the arrows don't really tell you whether you're sending data or not (though I've seen devices that animate the arrows while data is being transferred).
There's another box, what does that mean?
Sometimes you see a larger box to the left of the signal strength icon. This one usually says G, E, 1X, or Ev for GPRS, EDGE, 1xRTT, or EvDO. This icon says that the device can see that sort of network, but doesn't necessarily mean that it's connected. It's more of a, "This network is available," notification than anything else. The icon is often replaced with other notification icons, so you don't always see it. Its biggest benefit, in my opinion, is that it will tell you on a CDMA device whether you're currently getting 1xRTT speeds or the much faster EvDO speeds.
That's pretty much what I know on the subject. But if you have other questions, ask away. I'll see if I can find answers for you.