We know that there are those of you out there who would rather not have to pay AT&T an extra $20 per month for tethering when you're already paying upwards of $45 per month for a data plan. The trouble is that AT&T isn't really a fan of people avoiding their rules and fees, and the carrier has been cracking down on unauthorized tethering by jailbroken iPhone users. AT&T has been sending e-mails and SMS messages to customers asking them to stop the unauthorized tethering or else they would be charged.
AT&T actually has a very simple way to track down unauthorized tethering by iPhone users, because most tethering options use the same method as the official tethering, which routes your Internet traffic through an alternate APN (AT&T access point/router). This alternate APN is designed specifically to identify traffic as tethered, so AT&T can keep track of data usage and billing. Since many jailbreakers use the stock iPhone options for tethering, this makes it very easy for AT&T to track unauthorized usage and contact those in violation of their policies.
Luckily, one of the oldest and most popular apps in the Cydia app store for jailbroken iPhones is PdaNet from the good folks at June Fabrics. PdaNet has been around for the iPhone since the early days of jailbreaking (well before Apple offered a proprietary option), so the app has had plenty of time to mature and gain features. Right now, PdaNet for iPhone is on version 5.01, and best of all offers an option to hide usage from AT&T.
Of course, you'll need a jailbroken iPhone to take advantage of the app. Be warned that there are always risks associated with jailbreaking, so be sure you know what you're doing. PdaNet
is also available for Android, BlackBerry, and other mobile platforms.
source: Redmond Pie