You should know by now that an iPhone of the right vintage can be turned into a mobile hotspot—a portable router that pumps out a Wi-Fi signal on one side and talks to a mobile 3G broadband network on the other. The Personal Hotspot feature also lets iPhones starting with iOS 4. All iPhone 4 flavors can allow up to three Bluetooth devices to connect as part of a total of five connections of any kind among USB, Bluetooth, and Wi-Fi at any given time. The iPhone 3G or 3GS with 4. What you may not know is that the iOS 4. This lets any of those devices obtain an Internet connection from an iPhone with its sharing feature enabled. Yes, you can even connect one iPhone as a client to another acting as a server in this manner. Many other mobile devices can also tether over Bluetooth, as well as Mac OS X and Windows systems. Why connect with Bluetooth Bluetooth tethering has a set of advantages that might lead you to select it instead of Wi-Fi for routing your iOS device through an iPhone 4 Personal Hotspot. It also has a few drawbacks that might dissuade you. For iPhone 3G and 3GS users, this form of tethering also allows other iOS devices to share a connection, which was previously impossible. If either phone has iOS 4. On an iPhone 3GS with iOS 4. The key advantage of Bluetooth tethering is simplicity, especially with a streamlined pairing process for securely connecting two devices over Bluetooth that Apple added to the iOS with the 4. You can also likely save battery power on both the iPhone acting as a hotspot and the device or devices you to tether to it: Bluetooth should consume less power than Wi-Fi, even though modern Wi-Fi has a lot of built-in power-conserving features. When you turn on the feature on your iPhone, Wi-Fi sharing is only enabled for 90 seconds unless a device connects via Wi-Fi within that period. The same is true if you have Wi-Fi devices connected, and then disconnect or power down all of them: a 90-second countdown ensues. Instead of just pulling out your iPad, and waiting for it to connect, you have to first extract your iPhone, and navigate to the Personal Hotspot screen. Wi-Fi availability should automatically start up just by visiting that screen, although I found in testing that I sometimes had to tap the Personal Hotspot switch from On to Off and back to On again. Bluetooth sharing, in contrast, is always available with Personal Hotspot. The tablet should connect automatically. The iPad then connects. However, with Bluetooth, all the security is handled for you automatically. The pairing process confirms that no other party intercepted a key exchange; after that, strong encryption is used automatically with no data entry. The set-up Now, how would one set this up, I hear you ask? For setting up the Personal Hotspot, please consult our earlier coverage of that feature, which we linked to above. Carriers outside the U. On any other iOS device with version 4. It will appear by whatever name shows up when you sync in iTunes. You can change that in iTunes by clicking the name, and then typing in a new one. This works even on computers other than the one with which you sync your media and apps. If it does, tap Pair on each device. This security step prevents a third-party from intercepting traffic or pairing without permission. On your paired device, a special chain-link icon appears where a Wi-Fi signal strength meter typically shows up in the status bar at upper left. On both devices, the word Connected appears next to the name in the Bluetooth Devices list. This causes the device to reconnect. If that fails, try toggling the Personal Hotspot option on your phone from off to on. Tap Forget This Device, and it has no memory of how to connect. You can easily repair at will using the instructions above. His latest book is , just updated to include Personal Hotspot instructions.