I recently featured a video from CNET TV’s show Hacks. During the video, Brian Tong explains how to enable tethering on an iPhone using a mobile configuration file from a Web site called the iPhone Help Center by BenM.at.

As Tong notes in the video, and the BenM.at Web site warns, using a tethered iPhone may violate your cellular carrier’s service contract. For example, AT&T (currently the only iPhone carrier in the US) does not officially support tethering on the iPhone. They do however, support tethering on several other smartphones, including the Nokia E71m, Palm Centro, Blackberry Curve, and others. According to a CNET News.com article, AT&T does have “smartphone tethering plans, which offers Web connectivity for a laptop plus personal data usage for a smartphone, cost an additional $65 a month. The BlackBerry tethering plan costs $60 a month. Both services include 5GB of usage per month. Customers who exceed the allotted bucket of data usage are charged for overages on a per kilobyte basis.”

If a carrier detects that you’re using a tethered iPhone, they could conceivably charge you hefty additional fees, cut off your service, or both.