Why Tethering an iPhone 3G to a Laptop Doesn't Make Sense

There's been a lot of discussion on Mac-related websites about whether the iPhone 3G should support tethering to a laptop or desktop computer. For those of you who aren't familiar with the term, Wikipedia defines tethering as follows:

Tethering in cellular wireless is the connection of a non-mobile device (e.g. desktop computer, notebook computer, laptop computer), to a mobile device (e.g. cell phone) PDA like Palm Treo, Motorola Q, BlackBerry or Air Card for the purpose of wireless Internet access by the non-mobile "tethered" device.

Several phones already on sale on the AT&T, Verizon Wireless, and Sprint networks already support tethering. The unlimited data plan rates charged by the carriers for devices that support tethering are significantly higher than the proposed data plan rate for the iPhone 3G. As a result, some people who are planning to buy an iPhone 3G say that they will pay a higher data plan rate if they are allowed to tether their new iPhone to a laptop.

I don't think iPhone 3G owners would be happy with the performance of their iPhones if tethering were allowed. The reason is that tethering would consume a great deal more of the iPhone's power than most people realize.

I've made several trips from Trenton, NJ to New York Penn Station on the New Jersey Transit Northeast Corridor rail line over the past month. Each time I arrive in Manhattan, I am surprised that the battery level on my iPhone is low. The reason is that there are dead spots on the AT&T network that overlap the Northeast Corridor right of way, and the iPhone boosts its signal to stay connected when in those areas.

Imagine what would happen if you combine that with trying to maintain a constant 3G data connection and a constant Bluetooth connection to a laptop over a 75 to 90 minute trip. The battery will be substantially depleted by the time you step off the train.

Most of the 3G phones that support tethering also have replaceable batteries. The big reason why is that these handsets consume a lot more power than they would if they were sitting in your pocket, or even if you use it constantly on a voice call.

At this point in the development of battery technology, the form factor that Apple has chosen is the biggest single impediment to tethering the iPhone 3G to any other device.