The Personal Hotspot feature is also simple to setup: once you've changed your data plan over, which you can do right from , you simply enable the hotspot feature under Settings -> General -> Network, and a new Personal Hotspot sub-menu appears in the top level of Settings. From there you can turn the feature on or off and set a Wi-Fi password. Clients can then connect via Wi-Fi or Bluetooth, or you can plug your iPhone into your Mac via USB. A blue bar will appear at the top of the screen to let you know how many connections your iPhone currently has, even if you switch to other apps.

In terms of performance, USB actually appeared to provide the best throughput in my tests, which were conducted on a MacBook hooked up to an iPhone 4. The directed wired connection showed the highest download and upload speeds (Wi-Fi had lower latency, however). Bluetooth was by far the worst--no surprise, given that Bluetooth's transfer speed is in most cases slower than the phone's 3G connection. Wi-Fi held a firm middle ground in terms of speed, but it has the convenience factor of being wireless.

Unlike the Verizon iPhone 4, which supports up to five clients via Wi-Fi, the GSM iPhone supports a maximum of five clients spread through the various connection methods. For example, you can only have a maximum of three devices connected via Wi-Fi, but to that you can add other clients via Bluetooth or USB. And, of course, the more clients you add, the slower the connection will get as the devices jockey for bandwidth.

Surprisingly enough, if you've got an iPad in addition to your iPhone, you can connect it to the hotspot via either Wi-Fi or Bluetooth. (USB is out of the question, however, even if you're try using the iPad Camera Connection Kit.)

So, is the Personal Hotspot worth the cost? Giving up the unlimited data plan for my iPhone was a big move, but I went forward with it after running the numbers: over the last year and a half, I've rarely used more than 700MB a month on my iPhone's data plan, according to my AT&T bill. And after a year of having my iPad, I'd used just about 2GB of bandwidth on its 3G connection, according to the Usage section of Settings. Between the $5 per month I'd save with the 2GB data plan, and the $30 per month I could save by also dropping my iPad's unlimited 3G plan, I'd still come out ahead by $15 every month. Plus, I have the option of getting my MacBook online any place I can get a 3G signal. Your mileage may vary, of course, but it's worth looking into.