But despite that, you can't hook up the iPhone to a computer and share its cellular network connection, a curious deficit in its functionality. This ability, sharing a phone's EDGE or 3G connection with a computer via Bluetooth, USB, or Wi-Fi, is referred to as "tethering."

Using a phone that supports tethering, you'd be able to get your computer onto the Internet anywhere you have a cellular signal. That's handy on those occasions when you find yourself needing an Internet connection on your computer when you've only got it on your phone.

Whereas the older EDGE network is only capable of theoretical speeds of up to 236.8Kbps--in practice, quite slow even for cell phone use, let alone a Mac or PC--AT&T's newer 3G network currently boasts of theoretical speeds of up to 1.7Mbps, which is pretty fast whether you're on a phone or a computer. AT&T also claims that it has been able to achieve speeds of 7.2Mbps in its labs and plans to  by the end of 2009, though it's unknown whether or not existing hardware will be compatible.

As great as tethering sounds, there are several potential reasons why both Apple and AT&T may have been hesitant to bring it to the iPhone until now. First and foremost, it's quite evident that keeping Bluetooth or Wi-Fi turned on and transmitting data over the 3G network for extended periods of time can kill the battery life of the phone, perhaps necessitating that you charge it every couple of hours or keep it plugged in while tethering.

Furthermore, it's well known that AT&T doesn't have the most robust network in the business and its recently upgraded 3G network sometimes . It's hard to say how tethering will impact network performance, but the additional volume of data could have a negative impact.